jj thomson experiment set up

Structure of Atom

Cathode Ray Experiment

What is cathode ray tube.

A cathode-ray tube (CRT) is a vacuum tube in which an electron beam, deflected by applied electric or magnetic fields, produces a trace on a fluorescent screen.

The function of the cathode ray tube is to convert an electrical signal into a visual display. Cathode rays or streams of electron particles are quite easy to produce, electrons orbit every atom and move from atom to atom as an electric current.

Cathode ray tube, recommended videos.

J.J.Thomson Experiment

Apparatus Setup

Procedure of the experiment.

Frequently Asked Questions – FAQs

In a cathode ray tube, electrons are accelerated from one end of the tube to the other using an electric field. When the electrons hit the far end of the tube they give up all the energy they carry due to their speed and this is changed to other forms such as heat. A small amount of energy is transformed into X-rays.

The cathode ray tube (CRT), invented in 1897 by the German physicist Karl Ferdinand Braun, is an evacuated glass envelope containing an electron gun a source of electrons and a fluorescent light, usually with internal or external means to accelerate and redirect the electrons. Light is produced when electrons hit a fluorescent tube.

The electron beam is deflected and modulated in a manner that allows an image to appear on the projector. The picture may reflect electrical wave forms (oscilloscope), photographs (television, computer monitor), echoes of radar-detected aircraft, and so on. The single electron beam can be processed to show movable images in natural colours.

J. J. Thomson Experiment – The Discovery of Electron

The Cathode ray experiment was a result of English physicists named J. J. Thomson experimenting with cathode ray tubes. During his experiment he discovered electrons and it is one of the most important discoveries in the history of physics. He was even awarded a Nobel Prize in physics for this discovery and his work on the conduction of electricity in gases.

However, talking about the experiment, J. J. Thomson took a tube made of glass containing two pieces of metal as an electrode. The air inside the chamber was subjected to high voltage and electricity flowing through the air from the negative electrode to the positive electrode.

J. J. Thomson designed a glass tube that was partly evacuated, i.e. all the air had been drained out of the building. He then applied a high electric voltage at either end of the tube between two electrodes. He observed a particle stream (ray) coming out of the negatively charged electrode (cathode) to the positively charged electrode (anode). This ray is called a cathode ray and is called a cathode ray tube for the entire construction.

The experiment Cathode Ray Tube (CRT) conducted by J. J. Thomson, is one of the most well-known physical experiments that led to electron discovery . In addition, the experiment could describe characteristic properties, in essence, its affinity to positive charge, and its charge to mass ratio. This paper describes how J is simulated. J. Thomson experimented with Cathode Ray Tube.

The major contribution of this work is the new approach to modelling this experiment, using the equations of physical laws to describe the electrons’ motion with a great deal of accuracy and precision. The user can manipulate and record the movement of the electrons by assigning various values to the experimental parameters.

A Diagram of JJ.Thomson Cathode Ray Tube Experiment showing Electron Beam – A cathode-ray tube (CRT) is a large, sealed glass tube.

The apparatus of the experiment incorporated a tube made of glass containing two pieces of metals at the opposite ends which acted as an electrode. The two metal pieces were connected with an external voltage. The pressure of the gas inside the tube was lowered by evacuating the air.

Apparatus is set up by providing a high voltage source and evacuating the air to maintain the low pressure inside the tube.
High voltage is passed to the two metal pieces to ionize the air and make it a conductor of electricity.
The electricity starts flowing as the circuit was complete.
To identify the constituents of the ray produced by applying a high voltage to the tube, the dipole was set up as an add-on in the experiment.
The positive pole and negative pole were kept on either side of the discharge ray.
When the dipoles were applied, the ray was repelled by the negative pole and it was deflected towards the positive pole.
This was further confirmed by placing the phosphorescent substance at the end of the discharge ray. It glows when hit by a discharge ray. By carefully observing the places where fluorescence was observed, it was noted that the deflections were on the positive side. So the constituents of the discharge tube were negatively charged.

After completing the experiment J.J. Thomson concluded that rays were and are basically negatively charged particles present or moving around in a set of a positive charge. This theory further helped physicists in understanding the structure of an atom . And the significant observation that he made was that the characteristics of cathode rays or electrons did not depend on the material of electrodes or the nature of the gas present in the cathode ray tube. All in all, from all this we learn that the electrons are in fact the basic constituent of all the atoms.

Most of the mass of the atom and all of its positive charge are contained in a small nucleus, called a nucleus. The particle which is positively charged is called a proton. The greater part of an atom’s volume is empty space.

The number of electrons that are dispersed outside the nucleus is the same as the number of positively charged protons in the nucleus. This explains the electrical neutrality of an atom as a whole.

Uses of Cathode Ray Tube

Used as a most popular television (TV) display.
X-rays are produced when fast-moving cathode rays are stopped suddenly.
The screen of a cathode ray oscilloscope, and the monitor of a computer, are coated with fluorescent substances. When the cathode rays fall off the screen pictures are visible on the screen.

Frequently Asked Questions – FAQs

What are cathode ray tubes made of.

The cathode, or the emitter of electrons, is made of a caesium alloy. For many electronic vacuum tube systems, Cesium is used as a cathode, as it releases electrons readily when heated or hit by light.

Where can you find a cathode ray tube?

Cathode rays are streams of electrons observed in vacuum tubes (also called an electron beam or an e-beam). If an evacuated glass tube is fitted with two electrodes and a voltage is applied, it is observed that the glass opposite the negative electrode glows from the electrons emitted from the cathode.

How did JJ Thomson find the electron?

In the year 1897 J.J. Thomson invented the electron by playing with a tube that was Crookes, or cathode ray. He had shown that the cathode rays were charged negatively. Thomson realized that the accepted model of an atom did not account for the particles charged negatively or positively.

What are the properties of cathode rays?

They are formed in an evacuated tube via the negative electrode, or cathode, and move toward the anode. They journey straight and cast sharp shadows. They’ve got strength, and they can do the job. Electric and magnetic fields block them, and they have a negative charge.

What do you mean by cathode?

A device’s anode is the terminal on which current flows in from outside. A device’s cathode is the terminal from which current flows out. By present, we mean the traditional positive moment. Because electrons are charged negatively, positive current flowing in is the same as outflowing electrons.

Who discovered the cathode rays?

Studies of cathode-ray began in 1854 when the vacuum tube was improved by Heinrich Geissler, a glassblower and technical assistant to the German physicist Julius Plücker. In 1858, Plücker discovered cathode rays by sealing two electrodes inside the tube, evacuating the air and forcing it between the electrode’s electric current.

Which gas is used in the cathode ray experiment?

For better results in a cathode tube experiment, an evacuated (low pressure) tube is filled with hydrogen gas that is the lightest gas (maybe the lightest element) on ionization, giving the maximum charge value to the mass ratio (e / m ratio = 1.76 x 10 ^ 11 coulombs per kg).

What is the Colour of the cathode ray?

Cathode-ray tube (CRT), a vacuum tube which produces images when electron beams strike its phosphorescent surface. CRTs can be monochrome (using one electron gun) or coloured (using usually three electron guns to produce red, green, and blue images that render a multicoloured image when combined).

How cathode rays are formed?

Cathode rays come from the cathode because the cathode is charged negatively. So those rays strike and ionize the gas sample inside the container. The electrons that were ejected from gas ionization travel to the anode. These rays are electrons that are actually produced from the gas ionization inside the tube.

What are cathode rays made of?

Thomson showed that cathode rays were composed of a negatively charged particle, previously unknown, which was later named electron. To render an image on a screen, Cathode ray tubes (CRTs) use a focused beam of electrons deflected by electrical or magnetic fields.

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J.J. Thomson’s Cathode Ray Tube Experiment

In 1897, J.J. Thomson conducted a groundbreaking experiment using a cathode ray tube that revolutionized our understanding of atomic structure and subatomic particles . His experiment, conducted at Cambridge’s Cavendish Laboratory, involved manipulating cathode rays with electric and magnetic fields.

Thomson’s custom-made cathode-ray tubes, created by his skilled glassblower assistant Ebenezer Everett, played a crucial role in the success of his experiments. Through his observations, Thomson identified electrons , the first subatomic particles to be discovered, which were found to be 1,000 times smaller than a hydrogen atom.

This experiment provided evidence that cathode rays were composed of tiny particles, rather than waves in the now-rejected ether. It laid the foundation for our understanding of atomic structure and paved the way for advancements in particle physics . The significance of Thomson’s cathode ray tube experiment continues to resonate in the field of science.

Key Takeaways:

J.J. Thomson conducted a groundbreaking experiment using a cathode ray tube to study electrons and revolutionize our understanding of atomic structure .
Thomson’s experiments with the cathode ray tube provided evidence that cathode rays were composed of tiny particles, rather than waves in the now-rejected ether.
His discovery of electrons and the manipulation of cathode rays laid the foundation for our understanding of atomic structure and subatomic particles .
The quality of the cathode-ray tubes, as well as the skill of the glassblower, were crucial for the success of Thomson’s experiments.
Thomson’s experiments and subsequent theories inspired generations of physicists and led to further advancements in particle physics .

The Significance of J.J. Thomson’s Cathode Ray Tube Experiment

J.J. Thomson’s cathode ray tube experiment was a groundbreaking achievement that had a profound impact on our understanding of atomic structure and subatomic particles. His experiment provided evidence for the existence of electrons , the first subatomic particles to be discovered. Thomson’s manipulation of cathode rays and observations of their movement and behavior allowed him to determine the charge-to-mass ratio of electrons.

This experiment led Thomson to propose his “plum pudding” model of the atom, which suggested that atoms consisted of a positively charged “pudding” with negatively charged electrons embedded within it. Thomson’s experiment and subsequent theories about the nature of cathode rays and electrons paved the way for further advancements in particle physics and the development of the modern atomic model.

Thomson’s work inspired future physicists such as Ernest Rutherford and his famous gold foil experiment, which further elucidated the structure of the atom and led to the development of quantum physics. Thomson’s discovery of electrons and his contributions to modern physics solidify his place as one of the pioneers in the field.

“Thomson’s cathode ray tube experiment revolutionized our understanding of atomic structure and subatomic particles. His discovery of the charge-to-mass ratio of electrons laid the foundation for future advancements in the field of particle physics.” – Dr. Emily Johnson, Physics Professor

The Influence on Future Physicists

J.J. Thomson’s cathode ray tube experiment not only advanced our knowledge of atomic structure but also inspired future generations of physicists. His groundbreaking research and discoveries opened up new avenues of exploration within the field of particle physics and shaped the trajectory of scientific advancements.

Thomson’s experiment provided a solid foundation for further studies on the nature of electrons and subatomic particles. The understanding gained from his experiment led to the development of new theories and models that continue to be explored and refined by physicists to this day.

His contributions to the field of particle physics revolutionized our understanding of the microscopic world and set the stage for groundbreaking discoveries in the years to come. Without Thomson’s cathode ray tube experiment, our knowledge of atomic structure and subatomic particles would be vastly different, and the field of particle physics may not have progressed to the extent it has.

Contributions to Modern Physics

J.J. Thomson’s cathode ray tube experiment made significant contributions to modern physics . His discovery of electrons and the understanding of their charge-to-mass ratio laid the groundwork for further advancements in the field.

Thomson’s experiment and subsequent theories about the nature of cathode rays and electrons influenced the development of the modern atomic model, which has been refined and expanded upon over the years. His work paved the way for the development of quantum physics and the exploration of the fundamental building blocks of matter.

Thomson’s legacy as one of the pioneers of modern physics is evident in the continued study of particle physics and the development of new technologies based on his discoveries. His cathode ray tube experiment remains a cornerstone of scientific exploration and a testament to the importance of curiosity and experimentation in advancing our understanding of the universe.

Applications and Legacy of J.J. Thomson’s Cathode Ray Tube Experiment

The cathode ray tube experiment conducted by J.J. Thomson not only revolutionized our understanding of atomic structure and subatomic particles but also had a significant impact beyond the realm of scientific research.

One of the key applications of cathode ray tubes stemming from Thomson’s experiment is in television technology . These cathode ray tubes served as the display screens for early television sets, playing a crucial role in the development of this transformative technology.

Furthermore, cathode ray tubes found their use in oscilloscopes . These devices are essential for visualizing and measuring electrical waveforms, making them invaluable in various scientific and engineering fields.

Thomson’s pioneering work on the discovery of electrons and the development of the cathode ray tube also led to a groundbreaking advancement in medical imaging. By stopping fast-moving cathode rays, X-rays could be produced, enabling medical professionals to visualize internal structures and diagnose conditions accurately.

Recognizing the significance of his contributions, J.J. Thomson was awarded the Nobel Prize in Physics in 1906. This prestigious accolade serves as a testament to the profound impact his experiments had on the field of particle physics and the advancement of scientific knowledge.

Thomson’s cathode ray tube experiment and subsequent discoveries continue to inspire and influence future generations of scientists. His legacy is apparent in the continued study of particle physics and the development of new technologies based on his groundbreaking experiments and theories.

What was J.J. Thomson’s Cathode Ray Tube Experiment?

J.J. Thomson conducted a groundbreaking experiment using a cathode ray tube to study electrons and revolutionize our understanding of atomic structure.

When and where did the experiment take place?

The experiment took place in 1897 at Cambridge’s Cavendish Laboratory, where Thomson spent his scientific career.

How did Thomson manipulate the cathode rays?

Thomson was able to manipulate the cathode rays using electric and magnetic fields.

What did Thomson discover through his experiments?

Thomson was able to identify electrons, the first subatomic particles to be discovered, which were 1,000 times smaller than a hydrogen atom.

What evidence did Thomson’s experiments provide about cathode rays?

Thomson’s experiments provided evidence that cathode rays were composed of tiny particles, rather than waves in the now-rejected ether.

What was the significance of Thomson’s discovery of electrons?

Thomson’s discovery of electrons and the manipulation of cathode rays laid the foundation for our understanding of atomic structure and subatomic particles.

What was Thomson’s proposed model of the atom?

Thomson proposed the “plum pudding” model of the atom, which suggested that atoms consisted of a positively charged “pudding” with negatively charged electrons embedded within it.

What applications did cathode ray tubes have beyond scientific research?

Cathode ray tubes became integral parts of television technology , oscilloscopes , and also revolutionized medical imaging through the production of X-rays.

What was J.J. Thomson’s legacy in the field of particle physics?

Thomson’s work on the discovery of electrons and his profound impact on the field earned him the Nobel Prize in Physics in 1906, inspiring future scientists and advancing our understanding of subatomic particles and atomic structure.

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JJ Thompson’s Discovery of Electron: Cathode Ray Tube Experiment Explained

JJ Thomson discovered the electron in 1897 and there are tons of videos about it. However, most videos miss what JJ Thomson himself said was the motivating factor: a debate about how cathode rays move. Want to know not only how but why electrons were discovered?

The start of jj thomson, how thomson discovered electrons: trials and errors, thomson’s conclusion.

A short history of Thomson: Joseph John Thomson, JJ on papers, to friends, and even to his own son [1] , was born in Lancashire, England to a middle class bookseller. When he was 14 years old, Thomson planned to get an apprenticeship to a locomotive engineer but it had a long waiting list, so, he applied to and was accepted at that very young age to Owen’s college.

Thompson later recalled that, “the authorities at Owens College thought my admission was such a scandal – I expect they feared that students would soon be coming in perambulators – that they passed regulations raising the minimum age for admission, so that such a catastrophe should not happen again.

[2] ” While in school, his father died, and his family didn’t have enough money for the apprenticeship. Instead, he relied on scholarships at universities – ironically leading him to much greater fame in academia. In 1884, at the tender age of 28, Thomson applied to be the head of the Cavendish Research Institute.

He mostly applied as a lark and was as surprised as anyone to actually get the position! “I felt like a fisherman who…had casually cast a line in an unlikely spot and hooked a fish much too heavy for him to land. [3] ” Suddenly, he had incredible resources, stability and ability to research whatever he wished.

He ended up having an unerring ability to pinpoint interesting phenomena for himself and for others. In fact, a full eight of his research assistants and his son eventually earned Nobel Prizes, but, of course, like Thomson’s own Nobel Prize, that was in the future.

Why did J. J. Thomson discover the electron in 1897? Well, according to Thomson: “the discovery of the electron began with an attempt to explain the discrepancy between the behavior of cathode rays under magnetic and electric forces [4] .” What did he mean by that?

Well, a cathode ray, or a ray in a vacuum tube that emanates from the negative electrode, can be easily moved with a magnet. This gave a charismatic English chemist named William Crookes the crazy idea that the cathode ray was made of charged particles in 1879!

However, 5 years later, a young German scientist named Heinrich Hertz found that he could not get the beam to move with parallel plates, or with an electric field. Hertz decided that Crookes was wrong, if the cathode ray was made of charged particles then it should be attracted to a positive plate and repulsed from a negative plate.

Ergo, it couldn’t be particles, and Hertz decided it was probably some new kind of electromagnetic wave, like a new kind of ultraviolet light. Further, in 1892, Hertz accidentally discovered that cathode rays could tunnel through thin pieces of metal, which seemed like further proof that Crookes was so very wrong.

Then, in December of 1895, a French physicist named Jean Perrin used a magnet to direct a cathode ray into and out of an electroscope (called a Faraday cylinder) and measured its charge. Perrin wrote, “the Faraday cylinder became negatively charged when the cathode rays entered it, and only when they entered it; the cathode rays are thus charged with negative electricity .

[5] ” This is why JJ Thomson was so confused, he felt that Perrin had, “conclusive evidence that the rays carried a charge of negative electricity” except that, “Hertz found that when they were exposed to an electric force they were not deflected at all.” What was going on?

In 1896, Thomson wondered if there might have been something wrong with Hertz’s experiment with the two plates. Thomson knew that the cathode ray tubes that they had only work if there is a little air in the tube and the amount of air needed depended on the shape of the terminals.

Thomson wondered if the air affected the results. Through trial and error, Thomson found he could get a “stronger” beam by shooting it through a positive anode with a hole in it. With this system he could evacuate the tube to a much higher degree and, if the vacuum was good enough, the cathode ray was moved by electrically charged plates, “just as negatively electrified particles would be.

[6] ” (If you are wondering why the air affected it, the air became ionized in the high electric field and became conductive. The conductive air then acted like a Faraday cage shielding the beam from the electric field.)

As stated before, Heinrich Hertz also found that cathode rays could travel through thin solids. How could a particle do that? Thomson thought that maybe particles could go through a solid if they were moving really, really fast. But how to determine how fast a ray was moving?

Thomson made an electromagnetic gauntlet. First, Thomson put a magnet near the ray to deflect the ray one-way and plates with electric charge to deflect the ray the other way. He then added or reduced the charge on the plates so that the forces were balanced and the ray went in a straight line.

He knew that the force from the magnet depended on the charge of the particle, its speed and the magnetic field (given the letter B). He also knew that the electric force from the plates only depended on the charge of the particle and the Electric field. Since these forces were balanced, Thomson could determine the speed of the particles from the ratio of the two fields.

Thomson found speeds as big as 60,000 miles per second or almost one third of the speed of light. Thomson recalled, “In all cases when the cathode rays are produced their velocity is much greater than the velocity of any other moving body with which we are acquainted. [7] ”

Thomson then did something even more ingenious; he removed the magnetic field. Now, he had a beam of particles moving at a known speed with a single force on them. They would fall, as Thomson said, “like a bullet projected horizontally with a velocity v and falling under gravity [8] ”.

Note that these “bullets” are falling because of the force between their charge and the charges on the electric plates as gravity is too small on such light objects to be influential. By measuring the distance the bullets went he could determine the time they were in the tube and by the distance they “fell” Thomson could determine their acceleration.

Using F=ma Thomson determine the ratio of the charge on the particle to the mass (or e/m). He found some very interesting results. First, no matter what variables he changed in the experiment, the value of e/m was constant. “We may… use any kind of substance we please for the electrodes and fill the tube with gas of any kind and yet the value of e/m will remain the same.

[9] ” This was a revolutionary result. Thomson concluded that everything contained these tiny little things that he called corpuscles (and we call electrons). He also deduced that the “corpuscles” in one item are exactly the same as the “corpuscles” in another. So, for example, an oxygen molecule contains the same kind of electrons as a piece of gold! Atoms are the building blocks of matter but inside the atoms (called subatomic) are these tiny electrons that are the same for everything .

The other result he found was that the value of e/m was gigantic, 1,700 times bigger than the value for a charged Hydrogen atom, the object with the largest value of e/m before this experiment. So, either the “corpuscle” had a ridiculously large charge or it was, well, ridiculously small.

A student of Thomson’s named C. T. R. Wilson had experimented with slowly falling water droplets that found that the charge on the corpuscles were, to the accuracy of the experiment, the same as the charge on a charged Hydrogen atom! Thomson concluded that his corpuscles were just very, very, tiny, about 1,700 times smaller then the Hydrogen atom [1] . These experiments lead Thomson to come to some interesting conclusions:

Electrons are in everything and are well over a thousand times smaller then even the smallest atom.
Benjamin Franklin thought positive objects had too much “electrical fire” and negative had too little. Really, positive objects have too few electrons and negative have too many. Oops.
Although since Franklin, people thought current flowed from the positive side to the negative, really, the electrons are flowing the other way. When a person talks about “current” that flows from positive to negative they are talking about something that is not real! True “electric current” flows from negative to positive and is the real way the electrons move. [although by the time that people believed J.J. Thomson, it was too late to change our electronics, so people just decided to stick with “current” going the wrong way!]
Since electrons are tiny and in everything but most things have a neutral charge, and because solid objects are solid, the electrons must be swimming in a sea or soup of positive charges. Like raisons in a raison cookie.

The first three are still considered correct over one hundred years later. The forth theory, the “plum pudding model” named after a truly English “desert” with raisins in sweet bread that the English torture people with during Christmas, was proposed by Thomson in 1904.

In 1908, a former student of Thomson’snamed Ernest Rutherford was experimenting with radiation, and inadvertently demolished the “plum pudding model” in the process. However, before I can get into Rutherford’s gold foil experiment, I first want to talk about what was going on in France concurrent to Thomson’s experiments.

This is a story of how a new mother working mostly in a converted shed discovered and named the radium that Rutherford was experimenting with. That woman’s name was Marie Sklodowska Curie, and that story is next time on the Lightning Tamers.

[1] the current number is 1,836 but Thomson got pretty close

[1] p 14 “Flash of the Cathode Rays: A History of JJ Thomson’s Electron” Dahl

[2] Thompson, J.J. Recollections and Reflections p. 2 Referred to in Davis & Falconer JJ. Thompson and the Discovery of the Electron 2002 p. 3

[3] Thomson, Joseph John Recollections and Reflections p. 98 quoted in Davis, E.A & Falconer, Isabel JJ Thomson and the Discovery of the Electron 2002 p. 35

[4] Thomson, JJ Recollections and Reflections p. 332-3

[5] “New Experiments on the Kathode Rays” Jean Perrin, December 30, 1985 translation appeared in Nature, Volume 53, p 298-9, January 30, 1896

[6] Nobel Prize speech?

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Cathode Ray Experiment

The electric experiment by j.j. thomson.

J. J. Thomson was one of the great scientists of the 19th century; his inspired and innovative cathode ray experiment greatly contributed to our understanding of the modern world.

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Like most scientists of that era, he inspired generations of later physicists, from Einstein to Hawking .

His better-known research proved the existence of negatively charged particles, later called electrons, and earned him a deserved Nobel Prize for physics. This research led to further experiments by Bohr and Rutherford, leading to an understanding of the structure of the atom.

What is a Cathode Ray Tube?

Even without consciously realizing it, most of us are already aware of what a cathode ray tube is.

Look at any glowing neon sign or any ‘old-fashioned’ television set, and you are looking at the modern descendants of the cathode ray tube.

Physicists in the 19th century found out that if they constructed a glass tube with wires inserted in both ends, and pumped out as much of the air as they could, an electric charge passed across the tube from the wires would create a fluorescent glow. This cathode ray also became known as an ‘electron gun’.

Later and improved cathode ray experiments found that certain types of glass produced a fluorescent glow at the positive end of the tube. William Crookes discovered that a tube coated in a fluorescing material at the positive end, would produce a focused ‘dot’ when rays from the electron gun hit it.

With more experimentation, researchers found that the ‘cathode rays’ emitted from the cathode could not move around solid objects and so traveled in straight lines, a property of waves. However, other researchers, notably Crookes, argued that the focused nature of the beam meant that they had to be particles.

Physicists knew that the ray carried a negative charge but were not sure whether the charge could be separated from the ray. They debated whether the rays were waves or particles, as they seemed to exhibit some of the properties of both. In response, J. J. Thomson constructed some elegant experiments to find a definitive and comprehensive answer about the nature of cathode rays.

Thomson’s First Cathode Ray Experiment

Thomson had an inkling that the ‘rays’ emitted from the electron gun were inseparable from the latent charge, and decided to try and prove this by using a magnetic field.

His first experiment was to build a cathode ray tube with a metal cylinder on the end. This cylinder had two slits in it, leading to electrometers, which could measure small electric charges.

He found that by applying a magnetic field across the tube, there was no activity recorded by the electrometers and so the charge had been bent away by the magnet. This proved that the negative charge and the ray were inseparable and intertwined.

Thomson's Cathode Ray Second Experiment

Like all great scientists, he did not stop there, and developed the second stage of the experiment, to prove that the rays carried a negative charge. To prove this hypothesis, he attempted to deflect them with an electric field.

Earlier experiments had failed to back this up, but Thomson thought that the vacuum in the tube was not good enough, and found ways to improve greatly the quality.

For this, he constructed a slightly different cathode ray tube, with a fluorescent coating at one end and a near perfect vacuum. Halfway down the tube were two electric plates, producing a positive anode and a negative cathode, which he hoped would deflect the rays.

As he expected, the rays were deflected by the electric charge, proving beyond doubt that the rays were made up of charged particles carrying a negative charge. This result was a major discovery in itself, but Thomson resolved to understand more about the nature of these particles.

Thomson's Third Experiment

The third experiment was a brilliant piece of scientific deduction and shows how a series of experiments can gradually uncover truths.

Many great scientific discoveries involve performing a series of interconnected experiments, gradually accumulating data and proving a hypothesis .

He decided to try to work out the nature of the particles. They were too small to have their mass or charge calculated directly, but he attempted to deduce this from how much the particles were bent by electrical currents, of varying strengths.

Thomson found out that the charge to mass ratio was so large that the particles either carried a huge charge, or were a thousand times smaller than a hydrogen ion. He decided upon the latter and came up with the idea that the cathode rays were made of particles that emanated from within the atoms themselves, a very bold and innovative idea.

Later Developments

Thomson came up with the initial idea for the structure of the atom, postulating that it consisted of these negatively charged particles swimming in a sea of positive charge. His pupil, Rutherford, developed the idea and came up with the theory that the atom consisted of a positively charged nucleus surrounded by orbiting tiny negative particles, which he called electrons.

Quantum physics has shown things to be a little more complex than this but all quantum physicists owe their legacy to Thomson. Although atoms were known about, as apparently indivisible elementary particles, he was the first to postulate that they had a complicated internal structure.

Thomson's greatest gift to physics was not his experiments, but the next generation of great scientists who studied under him, including Rutherford, Oppenheimer and Aston. These great minds were inspired by him, marking him out as one of the grandfathers of modern physics.

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Martyn Shuttleworth (Sep 22, 2008). Cathode Ray Experiment. Retrieved Sep 14, 2024 from Explorable.com: https://explorable.com/cathode-ray-experiment

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Cathode Ray Tube experiment of J.J. Thomson

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J.J. Thompson performed a brilliant experiment which proved that atom consisted of charged subatomic particle(s). Before his work, atom was considered to be indestructible. However, when atoms were studied in large electric fields, evidences came up indicating that they consisted of subatomic particles.

The experiment

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Cathode Ray Tube Experiment

Key Questions

Thomson's experiments with cathode ray tubes helped him to discover the electron.

This ushered in a model of atomic structure referred to as the plum pudding model. I like to think of it like a sphere shaped chocolate chip cookie since plum pudding is not super popular in the US.

The cookie dough (they didn't know what it was yet) is positively charged and the chocolate chips (electrons) are negatively charged and scattered randomly throughout the cookie (atom). The positive and negative charges cancel producing a neutral atom.

J. J. Thomson (1856–1940) used this concept to determine the electron's charge-to-mass ratio in one of the classic physics experiments at the end of the 19th century. A voltage difference between the two anodes and cathodes in a highly evacuated glass container accelerates and shapes a beam of hot cathode electrons. The accelerating potential V determines the electrons' velocity v . The lost electric potential energy equals the acquired kinetic energy.

Only the electrons with a speed equal to E/B can pass straight through the crossed electric and magnetic fields and strike the fluorescent screen that glows at the point of impact.

The electron's charge-to-mass ratio is calculated to be

Its value is determined as follows:

The fact that Thomson only discovered one value for this number was an essential feature of his measurements. The cathode material, the remaining gas in the tube, or any other aspect of the experiment had no bearing on it. This independence demonstrated that the beam's constituent particles, now known as electrons, are a component of all matter. As a result, Thomson is credited with discovering the electron as the first elementary and truly fundamental particle.

The American scientist Robert Millikan could precisely measure the electron's charge 15 years after Thomson's investigations. This number and the charge-to-mass ratio made it possible to calculate the electron's mass. Currently, the most exact value that is obtainable is

Cathode Ray Tube (CRT)

Cathode ray tube definition.

A cathode ray tube or CRT is a device that produces cathode rays in a vacuum tube and accelerates them through a magnetic and electric field to strike a fluorescent screen to form images.

Cathode Ray Tube History

The eminent physicist Johann Hittorf discovered cathode rays in 1869 in Crookes tubes. Crookes tubes are partially vacuum tubes having two electrodes kept at a high potential difference to discharge cathode rays from the negatively charged electrode cathode. Arthur Schuster and William Crooks proved that cathode rays are deflected by electric and magnetic fields, respectively. In the year 1897, the English physicist J.J. Thomson’s experiments with cathode rays led to the discovery of the electron , the first subatomic particle to be discovered.

The earliest version of the cathode ray tube, Braun Tube, was invented in 1897 by the German physicist Ferdinand Braun. It employed a cold cathode for working. He used a phosphor-coated mica screen and a diaphragm to produce a visible dot. The cathode beam was deflected by a magnetic field only, in contrast to the discharge tube used earlier in the same year by J.J. Thomson, which employed only electrostatic deflection using two internal plates. Braun is also credited with the invention of the cathode ray tube oscilloscope, also known as Braun’s Electrometer.

In 1907, the cathode ray tube was first used in television when Russian scientist Boris Rosing passed a video signal through it to obtain geometric shapes on the screen. Earlier cathode ray tubes used cold cathodes. However, a hot cathode came into existence after being developed by John B. Johnson and Harry Weiner Weinhart of Western Electric. This type of cathode consists of a thin filament heated to a very high temperature by passing an electric current through it. It uses thermionic emissions in vacuum tubes to release electrons from a target.

The first commercial cathode ray tube television manufacture dates back to 1934 by the company Telefunken in Germany. This curved the path for large-scale manufacture and use of CRT TVs until the recent development of Liquid Crystal Displays, Light Emitting diodes, and Plasma TVs.

Cathode Ray Tube Description

The CRT is composed of three parts.

Electron Gun

This part produces a stream of electrons traveling at very high speeds by the process of thermionic emission. A thin filament is heated up by the passage of alternating current through it. It is used to heat the cathode, generally made of the metal cesium, which releases a stream of electrons when heated to temperatures of about 1750 F. The anode, which is the positively charged electrode, is placed a small distance away and is maintained at a high voltage which forces the cathode rays to gain considerably high accelerations as they move towards it.

The stream of electrons passes through a small aperture in the anode to land in the central part of the tube. There is a grid or a series of grids maintained at a variable potential, which control(s) the intensity of the electron beam reaching the anode. The brightness of the final image formed on the screen is also restricted thus. A monochrome CRT has a single electron gun, whereas a color CRT has three electron guns for the primary colors, red, green, and blue, which overlap among themselves to produce colored images.

Deflection System

The electron stream, after coming out of the anode, tends to spread out in the form of a cone. But it needs to be focused to form a sharp point on the screen. Also, its position on the screen should be as desired. This is achieved by subjecting the beam to magnetic and electric fields perpendicular to each other. The straight path of the beam then gets deflected, and it hits the screen at the desired point. It should be kept in mind that the anode gives it a considerable acceleration of the order of fractions of the speed of light. This endows the beam with very high amounts of energy.

Fluorescent CRT Screen

This part projects the image for the user’s view. It is given a coating of zinc sulfide or phosphorus which can produce fluorescence. When the highly energetic beam of electrons strikes it, its kinetic energy is converted to light energy, thus forming an illuminated spot on the screen. When complex signals are applied to the deflection system, the bright spot races across the screen horizontally and vertically, forming what is called the raster.

The raster scanning takes place in the same way as we would read a book. That is, from left to right, then go down and back to the left and move right to finish reading the line. This continues until the full screen is finished scanning. However, the CRT scan takes place so rapidly every second that the viewer cannot follow the actual movement of the dot but can see the whole image so produced.

Cathode Ray Tube Mechanism Video

Cathode ray tube experiment by j.j.thomson.

It was already known to the scientific fraternity that cathode rays were capable of depositing a charge, thereby proving them to be the carriers of some kind of charge. But they were not really sure whether this charge could be separated from the particles forming the rays. Hence, the celebrated English physicist J. J. Thomson devised an experiment to test the exact nature.

Thomson’s First CRT Experiment

Thomson took a cathode ray tube, and at the place where the electron beam was supposed to strike, he positioned a pair of metal cylinders having slits on them. The pair, in turn, was connected to an electrometer, a device for catching and measuring electric charges. Then, on operating the CRT, in the absence of any electric or magnetic fields, the beam of electrons traveled straight up to the cylinders, passed through the aptly positioned slits, and made the electrometer register a high amount of charge. So far, the result was quite an expected one.

In the next step, he put a magnet in the vicinity of the cathode ray path that set up a magnetic field. Now, as you may know, an electric field and a magnetic field can never act along the same line. Hence, the charged cathode rays get deflected from their path and give the slits a miss. The electrometer, hence, fails to register anything whatsoever. Thus, he concluded the cathode rays carry the charges along with them wherever they go, and it is impossible to separate the charges from the rays.

Thomson’s Second CRT Experiment

In his second attempt, Thomson tried to deflect the cathode rays by applying an electric field. It could prove the nature of the charge carried by them. There had been attempts before to achieve the end, but they had failed. He thought that if the streams are electrically charged, then they should be deflected by electric fields, but he could not explain why his setup failed to show any such movement.

He later came up with the idea that there was no change from the original path as the stream was covered by a conductor, that is, a layer of ionized air in this case. So he took great pains to make the interior of the tube as close to a vacuum as he could by drawing out all the residual air, and bravo! There was a pronounced deflection in the cathode rays. The great scientist had cleverly put two electrodes, positive and negative, halfway down the tube to produce the electric field. On observing that the beam deflected towards the anode, he could successfully prove that the cathode rays carried one and only one type of charge, negative.

Thomson’s Third CRT Experiment

Thomson tried to calculate the charge-to-mass ratio of the particles constituting the rays and found it to be exceptionally small. That implies the particles have either a very small mass or a very high charge. He decided on the former and gave a bold hypothesis that cathode rays were formed of particles emanating from the atom itself.

Experiment Summary

By using certain modifications in the regular CRT, Thomson’s cathode ray tube experiment proved that cathode rays consist of streams of negatively charged particles having smaller masses than that atoms. It was highly likely for them to be one of the components of atoms.

Cathode Ray Tube Applications

Oscilloscope.

It measures the changes in electrical voltage with time. If the horizontal plate is attached to a voltage source and the vertical to a clocking mechanism, then the variations in the magnitude of the voltage will show up on the CRT monitor in the form of a wave. With an increase in voltage, the line forming the wave shoots up while it comes down if the voltage is low. If, instead of a variable voltage source, the horizontal plates are connected to a circuit, then the arrangement can be used to detect any sudden change in its voltage. Thus, it can be used for troubleshooting purposes.

Televisions

Before the emergence of lightweight LCD and plasma TVs, all televisions were bulky and had cathode ray tubes in them. They had a very fast raster scan rate of about 1/50 th of a second. In a color TV, the persistence of the different colors would last for only the time between two consecutive scans. If it stayed longer, then the tube would produce blurred images. But if the effect of the colors ended before the next scan, then it gave rise to a flickering screen. Modern tube TVs use flat-screen CRTs, unlike their yesteryear counterparts.

Cathode Ray Tube Amusement Device

The predecessor to modern video games, the cathode ray tube amusement device gave the world the first gaming device. The CRT produced electronic signals in the form of a ray of light. Controller knobs in the tube were then used to adjust the trajectories of light so that it could hit on a target imprinted on a clear overlay attached to the CRT display screen. The game was conceptualized on World War II missile displays and created the effect of firing missiles at targets.

Other Applications

Cathode ray tube monitors are widely used as display devices in radars. However, the CRT computer monitor has gradually become obsolete with the introduction of TFT-LCD thin panel monitors.

Health Risks

Ionizing Radiation : CRTs can emit a small amount of ionizing radiation that needs to be kept under control by the Food and Drug Administration Regulations in 21 C.F.R. 1020.10. However, most CRTs manufactured after 2007 have much lesser emissions than the prescribed limit.

Flicker: Low refresh rates, 60Hz and below, can produce flicker in most people, although the susceptibility of eyesight to flicker varies from person to person.

Toxicity: Modern-day CRTs may have their rear glass tubes made of leaded glass, which is difficult to dispose of as they can cause an environmental hazard. Some of the older versions also contain cadmium and phosphorus, making the tubes highly toxic. Special cathode ray tube recycling processes fulfilling the norms of the United States Environmental Protection Agency should be followed.

Implosion: Very high levels of vacuum inside a CRT can cause it to implode if there is any damage to the covering glass. This is caused by the high atmospheric pressure, which forces the glass to crack and fly off at high speeds in all directions. Though modern CRTs have strong envelopes to prevent shattering, they should be handled very carefully.

Noise: The signal frequencies used to operate CRTs are of a very high range and are usually imperceptible to the human ear. However, small children can sometimes hear very high-pitched noises near CRT televisions. That is because they have a greater sensitivity to hearing.

The cathode ray tube was a useful invention in Science for the discovery of an important fundamental particle like an electron and also opened up newer arenas of research in atomic Physics. Until about the year 2000, it was the mainstay of televisions all over the world before being forced into oblivion due to the emergence of newer technologies.

https://en.wikipedia.org/wiki/Cathode_ray

https://www.chemteam.info/AtomicStructure/Disc-of-Electron-History.html

https://www.techtarget.com/whatis/definition/cathode-ray-tube-CRT

https://explorable.com/cathode-ray-experiment

http://www.scienceclarified.com/Ca-Ch/Cathode-Ray-Tube.html

Article was last reviewed on Tuesday, May 9, 2023

One response to “Cathode Ray Tube (CRT)”

I want to ask that in cathode ray tube tv why electrons are never finish which is on cathode while the material have limited electrons

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Subatomic science: JJ Thomson's discovery of the electron

Read about how JJ Thomson announced his discovery of the electron at the Royal Institution in this blog by our Head of Heritage and Collections.

JJ Thomson, while familiar to scientists, is not necessarily a name most people would recognise; however, anyone who has undertaken any science at school will have heard of an electron.

It is Thomson we have to thank for discovering this fundamental breakthrough in science and announcing his discovery to the world during a lecture here at the Royal Institution in 1897.

Painting of an elderly man with greying hair and a handlebar moustache wearing black academic robes, a white shirt and thin red scarf

What is an electron?

The technical definition is:

"An electron is a stable subatomic particle with a negative electrical charge. Unlike protons and neutrons, electrons are not constructed from even smaller components."

As a non-scientist this definition is something I have heard before but must confess is not something that means a great deal to me. It is an explanation in its basic form but doesn’t convey really what an electron is or what the impact of its discovery made

John Dalton's atomic theory

Prior to 1897, scientists had hypothesised about the makeup of the universe at the atomic and subatomic level but had not been able to prove any theories. The atom had been known about for many years.

In 1808, chemist John Dalton developed an argument that led to a realisation: that perhaps all matter, the things or objects that make up the universe are made of tiny, little bits.

These are fundamental and indivisible bits and named after the ancient Greek words ‘a’ meaning not and ‘tomos’ meaning cut therefore ‘atomos’ or uncuttable. Atoms.

JJ Thomson's cathode ray tube experiments

Thomson, a highly respected theoretical physics professor at Cambridge University, undertook a series of experiments designed to study the nature of electric discharge in a high-vacuum cathode-ray tube – he was attempting to solve a long-standing controversy regarding the nature of cathode rays, which occur when an electric current is driven through a vessel from which most of the air or other gas has been pumped out.

This was something that many scientists were investigating at the time. It was Thomson that made the breakthrough however, concluding through his experimentation that particles making up the rays were 1,000 times lighter than the lightest atom, proving that something smaller than atoms existed.

Thomson likened the composition of atoms to plum pudding, with negatively-charged ‘corpuscles’ dotted throughout a positively charged field.

A glass sphere with glass tubes at either end and metal bars inside

G Johnstone Stoney coins the term 'electron'

Thomson explained within his lecture all of his experiments and the results, never mentioning the word electron but instead sticking to corpuscles to explain these tiny particles in the same terms as biological cells (corpuscles are a minute body or cell in an organism).

Such would they have remained if not for the term 'electron' coined by G Johnstone Stoney who in 1891 denoted the unit of charge found in experiments that passed electrical current through chemicals.

It was then in 1897 after Thomson’s publication of his research that Irish physicist George Francis Fitzgerald suggested that the term be applied to Thomson's research instead of corpuscles to better describe these newly discovered subatomic particles.

JJ Thomson and the Royal Institution

Thomson had a long-standing relationship with the Royal Institution during his long academic career in Cambridge, lecturing many times on the development of physics through Discourses and educational lectures to all ages.

Thomson was a great friend of Sir William Henry Bragg and Sir William Lawrence Bragg, who jointly won the Nobel Prize in 1915 for the development of x-ray crystallography, and who were both former Director’s of the Royal Institution.

JJ Thomson's Nobel Prize

Thomson received the Nobel Prize for his work in Physics in 1906 and was knighted in 1908. The studies of nuclear organisation that continue even to this day and the further identification of elementary particles have all followed the accomplishments of Thomson and his discovery in 1897.

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J.J.. Thomson - Nobel Lecture: Electronic Waves

George Paget Thomson

Nobel lecture.

Nobel Lecture, June 7, 1938

Electronic Waves

Ever since last November, I have been wanting to express in person my gratitude to the generosity of Alfred Nobel, to whom I owe it that I am privileged to be here today, especially since illness prevented me from doing so at the proper time. The idealism which permeated his character led him to make his magnificent foundation for the benefit of a class of men with whose aims and viewpoint his own scientific instincts and ability had made him naturally sympathetic, but he was certainly at least as much concerned with helping science as a whole, as individual scientists. That his foundation has been as successful in the first as in the second, is due to the manner in which his wishes have been carried out. The Swedish people, under the leadership of the Royal Family, and through the medium of the Royal Academy of Sciences, have made the Nobel Prizes one of the chief causes of the growth of the prestige of science in the eyes of the world, which is a feature of our time. As a recipient of Nobel’s generosity I owe sincerest thanks to them as well as to him.

The goddess of learning is fabled to have sprung full-grown from the brain of Zeus, but it is seldom that a scientific conception is born in its final form, or owns a single parent. More often it is the product of a series of minds, each in turn modifying the ideas of those that came before, and providing material for those that come after. The electron is no exception.

Although Faraday does not seem to have realized it, his work on electrolysis, by showing the unitary character of the charges on atoms in solution, was the first step. Clerk Maxwell in 1873 used the phrase a “molecule of electricity” and von Helmholtz in 1881 speaking of Faraday’s work said “If we accept the hypothesis that elementary substances are composed of atoms, we cannot well avoid concluding that electricity also is divided into elementary portions which behave like atoms of electricity.” The hypothetical atom received a name in the same year when Johnstone Stoney of Dublin christened it “electron”, but so far the only property implied was an electron charge.

The last year of the nineteenth century saw the electron take a leading place amongst the conceptions of physics. It acquired not only mass but universality, it was not only electricity but an essential part of all matter. If among the many names associated with this advance I mention that of J.J. Thomson I hope you will forgive a natural pride. It is to the great work of Bohr that we owe the demonstration of the connection between electrons and Planck’s quantum which gave the electron a dynamics of its own. A few years later, Goudsmit and Uhlenbeck, following on an earlier suggestion by A.H. Compton showed that it was necessary to suppose that the electron had spin. Yet even with the properties of charge, mass, spin and a special mechanics to help it, the electron was unable to carry the burden of explaining the large and detailed mass of experimental data which had accumulated. L. de Broglie , working originally on a theory of radiation, produced as a kind of by-product the conception that any particle and in particular an electron, was associated with a system of waves. It is with these waves, formulated more precisely by Schrödinger, and modified by Dirac to cover the idea of spin, that the rest of my lecture will deal.

The first published experiments to confirm de Broglie’s theory were those of Davisson and Germer, but perhaps you will allow me to describe instead those to which my pupils and I were led by de Broglie’s epoch-making conception.

A narrow beam of cathode rays was transmitted through a thin film of matter. In the earliest experiment of the late Mr. Reid this film was of celluloid, in my own experiment of metal. In both, the thickness was of the order of 10 -6 cm. The scattered beam was received on a photographic plate normal to the beam, and when developed showed a pattern of rings, recalling optical halos and the Debye -Scherrer rings well known in the corresponding experiment with X-rays. An interference phenomenon is at once suggested. This would occur if each atom of the film scattered in phase a wavelet from an advancing wave associated with the electrons forming the cathode rays. Since the atoms in each small crystal of the metal are regularly spaced, the phases of the wavelets scattered in any fixed direction will have a definite relationship to one another. In some directions they will agree in phase and build up a strong scattered wave, in others they will destroy one another by interference. The strong waves are analogous to the beams of light diffracted by an optical grating. At the time, the arrangement of the atoms in celluloid was not known with certainty and only general conclusions could be drawn, but for the metals it had been determined previously by the use of X-rays. According to de Broglie’s theory the wavelength associated with an electron is h/mv which for the electrons used (cathode rays of 20 to 60,000 volts energy) comes out from 8 X 10 -9 to 5 X 10 -9 cm. I do not wish to trouble you with detailed figures and it will be enough to say that the patterns on the photographic plates agreed quantitatively, in all cases, with the distribution of strong scattered waves calculated by the method I have indicated. The agreement is good to the accuracy of the experiments which was about 1%. There is no adjustable constant, and the patterns reproduce not merely the general features of the X-ray patterns but details due to special arrangements of the crystals in the films which were known to occur from previous investigation by X-rays. Later work has amply confirmed this conclusion, and many thousands of photographs have been taken in my own and other laboratories without any disagreement with the theory being found. The accuracy has increased with the improvement of the apparatus, perhaps the most accurate work being that of v. Friesen of Uppsala who has used the method in a precision determination of e in which he reaches an accuracy of I in 1,000.

Before discussing the theoretical implications of these results there are two modifications of the experiments which should be mentioned. In the one, the electrons after passing through the film are subject to a uniform magnetic field which deflects them. It is found that the electrons whose impact on the plate forms the ring pattern are deflected equally with those which have passed through holes in the film. Thus the pattern is due to electrons which have preserved unchanged the property of being deflected by a magnet. This distinguishes the effect from anything produced by X-rays and shows that it is a true property of electrons. The other point is a practical one, to avoid the need for preparing the very thin films which are needed to transmit the electrons, an apparatus has been devised to work by reflection, the electrons striking the diffracting surface at a small glancing angle. It appears that in many cases the patterns so obtained are really due to electrons transmitted through small projections on the surface. In other cases, for example when the cleavage surface of a crystal is used, true reflection occurs from the Bragg planes.

The theory of de Broglie in the form given to it by Schrödinger is now known as wave mechanics and is the basis of atomic physics. It has been applied to a great variety of phenomena with success, but owing largely to mathematical difficulties there are not many cases in which an accurate comparison is possible between theory and experiment. The diffraction of fast electrons by crystals is by far the severest numerical test which has been made and it is therefore important to see just what conclusions the excellent agreement between theory and these experiments permits us to draw.

The calculations so far are identical with those in the corresponding case of the diffraction of X-rays. The only assumption made in determining the directions of the diffracted beams is that we have to deal with a train of wave of considerable depth and with a plane wave-front extending over a considerable number of atoms. The minimum extension of the wave system sideways and frontways can be found from the sharpness of the lines. Taking v. Friesen’s figures, it is at least 225 waves from back to front over a front of more than 200 Å each way.

But the real trouble comes when we consider the physical meaning of the waves. In fact, as we have seen, the electrons blacken the photographic plate at those places where the waves would be strong. Following Bohr, Born, and Schrödinger, we can express this by saying that the intensity of the waves at any place measures the probability of an electron manifesting itself there. This view is strengthened by measurements of the relative intensities of the rings, which agree well with calculations by Mott based on Schrödinger’s equation. Such a view, however successful as a formal statement is at variance with all ordinary ideas. Why should a particle appear only in certain places associated with a set of waves? Why should waves produce effects only through the medium of particles? For it must be emphasized that in these experiments each electron only sensitizes the photographic plate in one minute region, but in that region it has the same powers of penetration and photographic action as if it had never been diffracted. We cannot suppose that the energy is distributed throughout the waves as in a sound or water wave, the wave is only effective in the one place where the electron appears. The rest of it is a kind of phantom. Once the particle has appeared the wave disappears like a dream when the sleeper wakes. Yet the motion of the electron, unlike that of a Newtonian particle, is influenced by what happens over the whole front of the wave, as is shown by the effect of the size of the crystals on the sharpness of the patterns. The difference in point of view is fundamental, and we have to face a break with ordinary mechanical ideas. Particles have not a unique track, the energy in these waves is not continuously distributed, probability not determinism governs nature.

But while emphasizing this fundamental change in outlook, which I believe to represent an advance in physical conceptions, I should like to point out several ways in which the new phenomena fit the old framework better than is often realized. Take the case of the influence of the size of the crystals on the sharpness of the diffracted beams, which we have just mentioned. On the wave theory it is simply an example of the fact that a diffraction grating with only a few lines has a poor resolving power. Double the number of the lines and the sharpness of the diffracted beams is doubled also. However if there are already many lines, the angular change is small. But imagine a particle acted on by the material which forms the slits of the grating, and suppose the forces such as to deflect it into one of the diffracted beams. The forces due to the material round the slits near the one through which it passes will be the most important, an increase in the number of slits will affect the motion but the angular deflection due to adding successive slits will diminish as the numbers increase. The law is of a similar character, though no simple law of force would reproduce the wave effect quantitatively.

Similarly for the length of the wave train. If this were limited by a shutter moving so quickly as to let only a short wave train pass through, the wave theory would require that the velocity of the particle would be uncertain over a range increasing with the shortness of the wave train, and corresponding to the range of wavelengths shown by a Fourier analysis of the train. But the motion of the shutter might well be expected to alter the velocity of a particle passing through, just before it closed.

Again, on the new view it is purely a matter of chance in which of the diffracted beams of different orders an electron appears. If the phenomenon were expressed as the classical motion of a particle, this would have to depend on the initial motion of the particle, and there is no possibility of determining this initial motion without disturbing it hopelessly. There seems no reason why those who prefer it should not regard the diffraction of electrons as the motion of particles governed by laws which simulate the character of waves, but besides the rather artificial character of the law of motion, one has to ascribe importance to the detailed initial conditions of the motion which, as far as our present knowledge goes, are necessarily incapable of being determined. I am predisposed by nature in favour of the most mechanical explanations possible, but I feel that this view is rather clumsy and that it might be best, as it is certainly safer, to keep strictly to the facts and regard the wave equation as merely a way of predicting the result of experiments. Nevertheless, the view I have sketched is often a help in thinking of these problems. We are curiously near the position which Newton took over his theory of optics, long despised but now seen to be far nearer the truth than that of his rivals and successors.

“Those that are averse from assenting to any new Discoveries, but such as they can explain by an Hypothesis, may for the present suppose, that as Stones by falling upon water put the Water into an undulating Motion, and all Bodies by percussion excite vibrations in the Air: so the Rays of Light, by impinging on any refracting or reflecting Surface, excite vibrations in the refracting or reflecting Medium or Substance, much after the manner that vibrations are propagated in the Air for causing Sound, and move faster than the Rays so as to overtake them; and that when any Ray is in that part of the vibration which conspires with its Motion, it easily breaks through a refracting Surface, but when it is in the contrary part of the vibration which impedes its Motion, it is easily reflected; and, by consequence, that every Ray is successively disposed to be easily reflected, or easily transmitted, by every vibration which overtakes it. But whether this Hypothesis be true or false I do not here consider.”

Although the experiments in diffraction confirm so beautifully the de Broglie-Schrödinger wave theory, the position is less satisfactory as regards the extended theory due to Dirac. On this theory the electron possesses magnetic properties and the wave requires four quantities instead of one for its specification. This satisfies those needs of spectroscopy which led to the invention of the spinning electron. It suggests however that electronic waves could be polarized and that the polarized waves might interact with matter in an anisotropic manner. In fact detailed calculations by Mott indicate that if Dirac electrons of 140 kV energy are scattered twice through 90° by the nuclei of gold atoms the intensity of the scattered beam will differ by 16% according to whether the two scatterings are in the same or in opposite directions. Experiments by Dymond and by myself have established independently that no effect of this order of magnitude exists, when the scattering is done by gold foils. While there is a slight possibility that the circumnuclear electrons, or the organization of the atoms into crystals might effect the result, it seems very unlikely. Some of the theorists have arrived at results conflicting with Mott, but I understand that their work has been found to contain errors. At present there seems no explanation of this discrepancy which throws doubt on the validity of the Dirac equations in spite of their success in predicting the positive electron.

I should be sorry to leave you with the impression that electron diffraction was of interest only to those concerned with the fundamentals of physics. It has important practical applications to the study of surface effects. You know how X-ray diffraction has made it possible to determine the arrangement of the atoms in a great variety of solids and even liquids. X-rays are very penetrating, and any structure peculiar to the surface of a body will be likely to be overlooked, for its effect is swamped in that of the much greater mass of underlying material. Electrons only affect layers of a few atoms, or at most tens of atoms, in thickness, and so are eminently suited for the purpose. The position of the beams diffracted from a surface enables us, at least in many cases, to determine the arrangement of the atoms in the surface. Among the many cases which have already been studied I have only time to refer to one, the state of the surface of polished metals. Many years ago Sir George Beilby suggested that this resembled a supercooled liquid which had flowed under the stress of polishing. A series of experiments by electron diffraction carried out at the Imperial College in London has confirmed this conclusion. The most recent work due to Dr. Cochrane has shown that though this amorphous layer is stable at ordinary temperature as long as it remains fixed to the mass of the metal, it is unstable when removed, and recrystalizes after a few hours. Work by Professor Finch on these lines has led to valuable conclusions as to the wear on the surfaces of cylinders and pistons in petrol engines.

It is in keeping with the universal character of physical science that this single small branch of it should touch on the one hand on the fundamentals of scientific philosophy and on the other, questions of everyday life.

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suggested that they do. He advanced the idea that cathode rays are really streams of very small pieces of atoms. Three experiments led him to this.: of an 1895 experiment by Jean Perrin, Thomson built a ending in a pair of metal cylinders with a slit in them. These cylinders were in turn connected to an electrometer, a device for catching and measuring electrical charge. Perrin had found that cathode rays deposited an electric charge. Thomson wanted to see if, by bending the rays with a magnet, he could separate the charge from the rays. He found that when the rays entered the slit in the cylinders, the electrometer measured a large amount of negative charge. The electrometer did not register much electric charge if the rays were bent so they would not enter the slit. As Thomson saw it, the negative charge and the cathode rays must somehow be stuck together: you cannot separate the charge from the rays.
.		when physicists tried to bend cathode rays with an electric field. Now Thomson thought of a new approach. A charged particle will normally curve as it moves through an electric field, but not if it is surrounded by a conductor (a sheath of copper, for example). Thomson suspected that the traces of gas remaining in the tube were being turned into an electrical conductor by the cathode rays themselves. To test this idea, he took great pains to extract nearly all of the gas from a tube, and found that now the cathode rays did bend in an electric field after all.
	from these two experiments, "I can see no escape from the conclusion that [cathode rays] are charges of negative electricity carried by particles of matter." But, he continued, "What are these particles? are they atoms, or molecules, or matter in a still finer state of subdivision?"
.		sought to determine the basic properties of the particles. Although he couldn't measure directly the mass or the electric charge of such a particle, he could measure how much the rays were bent by a magnetic field, and how much energy they carried. From this data he could calculate the of the mass of a particle to its electric charge ( / ). He collected data using a variety of tubes and using different gases.
.		Just as Emil Wiechert had reported earlier that year, the mass-to-charge ratio for cathode rays turned out to be far smaller than that of a charged hydrogen atom--more than one thousand times smaller. Either the cathode rays carried an enormous charge (as compared with a charged atom), or else they were amazingly light relative to their charge. was settled by . Experimenting on how cathode rays penetrate gases, he showed that if cathode rays were particles they had to have a mass very much smaller than the mass of any atom. The proof was far from conclusive. But experiments by others in the next two years yielded an independent measurement of the value of the charge ( ) and confirmed this remarkable conclusion.
the hypothesis that "we have in the cathode rays matter in a new state, a state in which the subdivision of matter is carried very much further than in the ordinary gaseous state: a state in which all matter... is of one and the same kind; this matter being the substance from which all the chemical elements are built up."
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Cathode Ray Experiment

Cathode Ray Experiment , also known as the Crookes tube experiment , is a historically significant experiment in the field of physics that helped scientists understand the nature of electrons. English scientist Sir J.J. Thomson performed an experiment using a Cathode Ray Tube, which led to the discovery of an electron.

In this article, we will discuss this significant experiment, including details of the Cathode Ray Tube, the procedure of the experiment, and J.J. Thomson’s observations, which led to one of the greatest discoveries in the field of science.

Table of Content

What is the Cathode Ray Experiment?

What is Cathode Ray Tube (CRT)?

Experiment Setup

Applications of Cathode Ray Experiment

Limitations of the Cathode Ray Experiment

What is Cathode Ray Experiment?

Cathode Ray Experiment, also known as the Cathode Ray Tube (CRT) Experiment, is a fundamental experiment in the history of physics that played a crucial role in understanding the nature of electrons and contributed to the development of modern electronics and television technology.

The experiment was first conducted by Sir William Crookes in the 1870s and later improved upon by scientists like J.J. Thomson in the late 19 th and early 20 th centuries.

Who is J.J. Thomson?

Joseph John Thomson, often called J.J. Thomson, was a British physicist celebrated for winning the Nobel Prize in Physics in 1906 for his research on how electricity moves through gases. His notable achievement was the discovery of the electron during the Cathode Ray Experiment.

A Cathode Ray Tube (CRT) is a special glass tube that played a big part in J.J. Thomson’s important experiment. This clever device helped scientists understand tiny particles that make up atoms.

Structure of CRT

CRT has a simple structure. It’s a sealed glass tube with two electrodes at each end – one is called the cathode (negative), and the other is the anode (positive). When these electrodes are connected to power, they create an electric field inside the tube. The tube is made empty, like a vacuum, so there’s no air inside.

The vacuum is essential because it lets cathode rays move in a straight line from the cathode to the anode without any interference from air. This controlled setup helps scientists study the behavior of cathode rays in different situations. The CRT is a key tool that led to important discoveries about the tiniest building blocks of matter.

Cathode Ray Experiment Setup

Below is the detailed setup for the Cathode Ray Tube Experiment with the elements used along with the diagram:

Cathode Ray Tube (CRT): A sealed glass tube with a cathode and anode at either end.
Cathode: A negatively charged electrode inside the CRT.
Anode: A positively charged electrode inside the CRT.
High Voltage Generator: A power supply capable of providing a high voltage between the cathode and anode.
Vacuum Pump: A pump to evacuate air from the CRT to create a low-pressure environment.
Discharge Tube: The entire CRT assembly including the cathode, anode, and vacuum space.
Perforated Anode Disk: Placed at the anode end to allow some cathode rays to pass through.

Procedure of Experiment

Below is the procedure steps for the experiment with the perspective of the JJ Thomson:

JJ Thomson created a sealed cathode ray tube with minimal air inside.
Connected the tube to a power source, causing electrons (cathode rays) to shoot out.
Observed electrons moving in straight lines inside the vacuum of the tube.
Introduced an electric field by adjusting the power, causing electrons to change their path.
Experimented with magnets, observing electrons being affected and swerving in response.
Adjusted power settings to observe changes in electron movement, establishing consistent patterns.
Systematically recorded electron behavior in various situations.
Determined the charge-to-size ratio of electrons, making a significant discovery.
Concluded that cathode rays were composed of tiny particles known as electrons.
Thomson’s discovery revolutionized understanding of the microscopic world’s building blocks.

Observation of Cathode Ray Experiment

In the Cathode Ray Experiment, J.J. Thomson made a ground breaking observation i.e., when cathode rays encountered electric and magnetic fields, they exhibited intriguing behavior. Thomson noticed their deflection, and the direction of this deflection pointed to a negative charge. This pivotal observation led Thomson to the groundbreaking conclusion that cathode rays were composed of negatively charged particles, now recognized as electrons.

Conclusion of Cathode Ray Experiment

Cathode Ray Experiment marked a revolutionary moment in the realm of science. J.J. Thomson’s demonstration of cathode ray deflection and the identification of these rays as negatively charged particles conclusively affirmed the existence of subatomic particles. This groundbreaking experiment transformed our comprehension of atomic structure, shattering the notion that atoms were indivisible. Instead, Thomson’s work revealed the presence of smaller components within atoms. This pivotal episode in the history of physics not only altered fundamental perspectives but also laid the foundation for subsequent advancements in the field.

The Cathode Ray Experiment, conducted by Sir J.J. Thomson in 1897, led to several significant applications and advancements in various fields:

Discovery of the Electron: The most direct outcome of the Cathode Ray Experiment was the discovery of the electron, a fundamental component of atoms. This discovery was pivotal in the development of atomic theory and quantum physics.
Television and Computer Monitors: The technology behind cathode ray tubes (CRTs) was essential in the development of early television and computer monitors. These devices used electron beams, controlled and focused by magnetic or electric fields, to illuminate phosphors on the screen, creating images.
Medical Imaging: Cathode ray technology found applications in medical imaging, particularly in early forms of X-ray machines and later in more advanced imaging technologies.
Electron Microscopy: The principles discovered in the Cathode Ray Experiment were integral to the development of electron microscopy, which uses a beam of electrons to create an image of a specimen. This technology allows for much higher resolution than traditional light microscopy.

Limitations of Cathode Ray Experiment

The Cathode Ray Experiment, while groundbreaking in its time, had several limitations:

Lack of Precise Measurement Tools: At the time of Thomson’s experiments, the precision and accuracy of measurement tools were limited. This meant that the measurements of the charge-to-mass ratio of electrons were not as accurate as what can be achieved with modern equipment.
Incomplete Understanding of Subatomic Particles: Thomson’s experiment was conducted at a time when the structure of the atom was not fully understood. This meant that while the experiment led to the discovery of the electron, it did not provide a complete picture of subatomic particles and their interactions.
Limited Control over Experimental Conditions: The vacuum technology and methods to control the electric and magnetic fields in Thomson’s time were rudimentary compared to today’s standards. This limited the ability to control experimental conditions precisely.
Atomic Structure
Discovery of Electrons

Cathode Ray Experiment – FAQs

J.J. Thomson, whose full name is Joseph John Thomson, was a British physicist born on December 18, 1856, in Cheetham Hill, Manchester, England, and he passed away on August 30, 1940. He is best known for his discovery of the electron, a fundamental subatomic particle.

What are Cathode Rays?

Cathode rays are streams of electrons observed in a vacuum when a high voltage is applied between electrodes in a cathode ray tube (CRT). These rays were first discovered and studied by J.J. Thomson in the late 19th century.

What was the Cathode Ray Experiment?

The cathode ray experiment, conducted by J.J. Thomson in the late 19th century, was a series of experiments that led to the discovery of electrons and provided crucial insights into the nature of subatomic particles.

What are Two Conclusions of the Cathode Ray Experiment?

Two conclusion of Cathode Ray Experiment are: Cathode rays are streams of negatively charged particles (electrons). These particles are fundamental components of all atoms.

Why did J.J. Thomson Experimented with Cathode?

J.J. Thomson experimented with cathode rays to investigate their nature and to understand the internal structure of atoms.

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Cathode Ray Experiment by JJ.Thomson (CRT)
The experiment Cathode Ray Tube (CRT) conducted by J. J. Thomson, is one of the most well-known physical experiments that led to electron discovery. In addition, the experiment could describe characteristic properties, in essence, its affinity to positive charge, and its charge to mass ratio. This paper describes how J is simulated.
Discovery of the Electron: Cathode Ray Tube Experiment
To see all my Chemistry videos, check outhttp://socratic.org/chemistryJ.J. Thompson discovered the electron, the first of the subatomic particles, using the ...
J.J. Thomson's Cathode Ray Tube Experiment
In 1897, J.J. Thomson conducted a groundbreaking experiment using a cathode ray tube that revolutionized our understanding of atomic structure and subatomic particles. His experiment, conducted at Cambridge's Cavendish Laboratory, involved manipulating cathode rays with electric and magnetic fields. Thomson's custom-made cathode-ray tubes ...
JJ Thomson, electrons and the Cathode Ray Tube
A year earlier, in 1936, Thomson wrote an autobiography called "Recollections and Reflections". He died in 1940, buried near Isaac Newton and Charles Darwin. JJ stands for "Joseph John". Strangely, another author with the name JJ Thomson wrote a book with the same name in 1975. Thomson had many famous students, including Ernest Rutherford.
Discovery of electron
Discovery of electron through cathode ray tube experiment by j.j thomson is explained by Particle physicist, Brian Cox.#cavendishlaboratory #jjthompsonmodelo...
J.J. Thomson's Cathode Ray Tube Experiment
Yes, J.J. Thomson used cathode rays. He used them in his experiments with cathode ray tubes in order to determine what cathode rays were composed of. He found that they were composed of a ...
JJ Thomson Cathode Ray Tube Experiment: the Discovery of the Electron
In 1897, JJ Thomson discovered the electron in his famous cathode ray tube experiment. How did it work and why did Thomson do the experiment in the first pl...
JJ Thompson's Discovery of Electron: Cathode Ray Tube Experiment Explained
In 1896, Thomson wondered if there might have been something wrong with Hertz's experiment with the two plates. Thomson knew that the cathode ray tubes that they had only work if there is a little air in the tube and the amount of air needed depended on the shape of the terminals. Thomson wondered if the air affected the results.
Cathode Ray Experiment by J. J. Thomson
Thomson's First Cathode Ray Experiment. Thomson had an inkling that the 'rays' emitted from the electron gun were inseparable from the latent charge, and decided to try and prove this by using a magnetic field. His first experiment was to build a cathode ray tube with a metal cylinder on the end. This cylinder had two slits in it, leading ...
Cathode Ray Tube experiment of J.J. Thomson
J.J. Thompson performed a brilliant experiment which proved that atom consisted of charged subatomic particle(s). Before his work, atom was considered to be indestructible. However, when atoms were studied in large electric fields, evidences came up indicating that they consisted of subatomic particles. Add explanation that you think will be helpful to other members.
Cathode Ray Tube Experiment
Question #cd7c0. JJ Thompson did an experiment using a cathode ray tube and found that electrons passed from the surface of the cathode and accelerate toward the positively charged anode. The anode absorbed many electrons, but is the anode has slits some electrons will pass through. He is credited with the first discovery of the electron.
Thomson's e/m Experiment
The two forces are equal in strength for the given field strengths E and B for a specific value of v, for which the total force is zero, given by. J. J. Thomson (1856-1940) used this concept to determine the electron's charge-to-mass ratio in one of the classic physics experiments at the end of the 19th century.
Cathode Ray Tube (CRT)
In the year 1897, the English physicist J.J. Thomson's experiments with cathode rays led to the discovery of the electron, the first subatomic particle to be discovered. ... In the next step, he put a magnet in the vicinity of the cathode ray path that set up a magnetic field. Now, as you may know, an electric field and a magnetic field can ...
Khan Academy
If you're seeing this message, it means we're having trouble loading external resources on our website. If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.
J. J. Thomson's CRT Experiment
This video is an explanation of J. J. Thomson's cathode ray tube experiment--an experiment in which the electron was discovered, along with its charge-to-mas...
Subatomic science: JJ Thomson's discovery of the electron
JJ Thomson's cathode ray tube experiments. Thomson, a highly respected theoretical physics professor at Cambridge University, undertook a series of experiments designed to study the nature of electric discharge in a high-vacuum cathode-ray tube - he was attempting to solve a long-standing controversy regarding the nature of cathode rays, which occur when an electric current is driven through ...
Experiments by J.J. Thomson in 1897 led to the discovery of a ...
Brought to you by the Center for History of Physics of the American Institute of Physics. 1997- 2024 American Institute of Physics. An exhibit by the AIP Center for History of Physics with text, animations and voice about J.J. Thomson's 1897 experiments which helped bring understanding of the electron as a fundamental unit of matter.
J.J. Thomson
The first published experiments to confirm de Broglie's theory were those of Davisson and Germer, but perhaps you will allow me to describe instead those to which my pupils and I were led by de Broglie's epoch-making conception. ... MLA style: J.J. Thomson - Nobel Lecture. NobelPrize.org. Nobel Prize Outreach AB 2024. Mon. 9 Sep 2024 ...
Three Experiments and One Big Idea
Three experiments led him to this.: irst, in a variation of an 1895 experiment by Jean Perrin, Thomson built a cathode ray tube ending in a pair of metal cylinders with a slit in them. These cylinders were in turn connected to an electrometer, a device for catching and measuring electrical charge. Perrin had found that cathode rays deposited an ...
Demystifying Cathode Rays: J.J. Thomson's Groundbreaking Experiment
📢 Receive Comprehensive Mathematics Practice Papers Weekly for FREE 😊Click this link to get: ️ ️ ️ https://iitutor.com/email-list/ ️ ️ ️In this ...
Cathode Ray Experiment by J.J. Thomson
Cathode Ray Experiment, also known as the Crookes tube experiment, is a historically significant experiment in the field of physics that helped scientists understand the nature of electrons.English scientist Sir J.J. Thomson performed an experiment using a Cathode Ray Tube, which led to the discovery of an electron.. In this article, we will discuss this significant experiment, including ...

Cathode Ray Experiment

Table of Contents

Apparatus Setup

J. J. Thomson Experiment – The Discovery of Electron

Uses of Cathode Ray Tube

Frequently Asked Questions – FAQs

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How did JJ Thomson find the electron?

What are the properties of cathode rays?

What do you mean by cathode?

Who discovered the cathode rays?

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What is the Colour of the cathode ray?

How cathode rays are formed?

What are cathode rays made of?

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J.J. Thomson’s Cathode Ray Tube Experiment

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The Significance of J.J. Thomson’s Cathode Ray Tube Experiment

The Influence on Future Physicists

Contributions to Modern Physics

Applications and Legacy of J.J. Thomson’s Cathode Ray Tube Experiment

What was J.J. Thomson’s Cathode Ray Tube Experiment?

When and where did the experiment take place?

How did Thomson manipulate the cathode rays?

What did Thomson discover through his experiments?

What evidence did Thomson’s experiments provide about cathode rays?

What was the significance of Thomson’s discovery of electrons?

What was Thomson’s proposed model of the atom?

What applications did cathode ray tubes have beyond scientific research?

What was J.J. Thomson’s legacy in the field of particle physics?

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Cathode Ray Experiment

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