j.j. thomson experiment explained

• 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.

Table of Contents

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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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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Discovering the electron: JJ Thomson and the Cathode Ray Tube

Concept Introduction: JJ Thomson and the Discovery of the Electron

The discovery of the electron was an important step for physics, chemistry, and all fields of science. JJ Thomson made the discovery using the cathode ray tube. Learn all about the discovery, the importance of the discovery, and JJ Thomson in this tutorial article.

Further Reading on the Electron

Electron Orbital and Electron Shapes Writing Electron Configurations Electron Shells What are valence electrons? Electron Affinity Aufbau Principle

Who was JJ Thomson?

JJ Thomson was an English physicist who is credited with discovery of the electron in 1897. Thompson was born in December 1856 in Manchester, England and was educated at the University of Manchester and then the University of Cambridge, graduating with a degree in mathematics. Thompson made the switch to physics a few years later and began studying the properties of cathode rays. In addition to this work, Thomson also performed the first-ever mass spectrometr y experiments, discovered the first isotope and made important contributions both to the understanding of positively charged particles and electrical conductivity in gases.

Thomson did most of this work while leading the famed Cavendish Laboratory at the University of Cambridge. Although he received the Nobel Prize in physics and not chemistry, Thomson’s contributions to the field of chemistry are numerous. For instance, the discovery of the electron was vital to the development of chemistry today, and it was the first subatomic particle to be discovered. The proton and the neutron would soon follow as the full structure of the atom was discovered.

What is a cathode ray tube and why was it important?

Prior to the discovery of the electron, several scientists suggested that atoms consisted of smaller pieces. Yet until Thomson, no one had determined what these might be. Cathode rays played a critical role in unlocking this mystery. Thomson determined that charged particles much lighter than atoms , particles that we now call electrons made up cathode rays. Cathode rays form when electrons emit from one electrode and travel to another. The transfer occurs due to the application of a voltage in vacuum. Thomson also determined the mass to charge ratio of the electron using a cathode ray tube, another significant discovery.

How did Thomson make these discoveries?

Thomson was able to deflect the cathode ray towards a positively charged plate deduce that the particles in the beam were negatively charged. Then Thomson measured how much various strengths of magnetic fields bent the particles. Using this information Thomson determined the mass to charge ratio of an electron. These were the two critical pieces of information that lead to the discovery of the electron. Thomson was now able to determine that the particles in question were much smaller than atoms, but still highly charged. He finally proved atoms consisted of smaller components, something scientists puzzled over for a long time. Thomson called the particle “corpuscles” , not an electron. George Francis Fitzgerald suggested the name electron.

Why was the discovery of the electron important?

The discovery of the electron was the first step in a long journey towards a better understanding of the atom and chemical bonding. Although Thomson didn’t know it, the electron would turn out to be one of the most important particles in chemistry. We now know the electron forms the basis of all chemical bonds. In turn chemical bonds are essential to the reactions taking place around us every day. Thomson’s work provided the foundation for the work done by many other important scientists such as Einstein, Schrodinger, and Feynman.

Interesting Facts about JJ Thomson

Not only did Thomson receive the Nobel Prize in physics in 1906 , but his son Sir George Paget Thomson won the prize in 1937. 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 the Electron: Further Reading

Protons, Neutrons & Electrons Discovering the nucleus with gold foil Millikan oil drop experiment Phase Diagrams

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?

Table of Contents

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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• Cathode Ray Experiment

What are Cathode Rays?

Cathode rays are a beam of negatively charged electrons traveling from the negative end of an electrode to the positive end within a vacuum, across a potential difference between the electrodes.

How Do the Cathode Rays Work?

The cathode is a negative electrode, Anode is the positive electrode. Since electrons are repelled by the negative electrode, the cathode is the source of cathode rays inside a vacuum environment. When a potential difference is applied, the electrons jump to an excited state and travel at high speeds to jump back-and-forth inside the vacuum glass chamber and when some cathode rays certain molecules of the cathode screen, they emit light energy. A wire is connected from anode to cathode to complete the electrical circuit.

Construction of a Cathode Ray Tube

Its Basic Components are: -

Electron Gun Assembly: - It is the source of the electron beams. The electron gun has a heater, cathode, pre-accelerating anode, focusing anode and accelerating anode.

Deflecting Plates: - They produce a uniform electrostatic field only in one direction, and accelerate particles in only one direction.

Screen: - The inner layer of the screen is coated with phosphorus, and produces fluorescence when cathode rays hit the screen by a process of phosphorus excitation.

Aquadag: - It is an aqueous solution of graphite used to collect the secondary emitted electrons which are required to keep the cathode ray in electrical equilibrium.

What is the Cathode Ray Tube Experiment?

In 1897, great physician J.J. Thompson, conducted his first cathode ray tube experiment to prove that rays emitted from an electron gun are inseparable from the latent charge. He built his cathode ray tube with a metal cylinder on the other end. The metal had two small diversions(slits), leading to an electrometer that could measure a small electric charge. From the first experiment, he discovered that the electrometers stopped measuring electric charge. From this, he deduced that the electric charge and the cathode rays must be combined and are the same entity.

Then he conducted a Second experiment, to prove the charge carried by the cathode rays was negative or positive. Now, he put a negatively charged metal plate on one side of the cathode rays to go past the anode, and a positively charged metal plate on the other side. Instead of an electrometer at one end of the Cathode Ray Tube, he used a fluorescent coated tube that would glow where the cathode ray hit it. When the charged metal plates were introduced he found that the cathode rays bent away from the negative plate and towards the positive plate. This proved that the cathode rays were negatively charged.

Then he performed the third experiment, to know the nature of the particles and reduce the mass of the particles as they had too small of a mass to be calculated directly. For the experiment, he used the cathode ray tube and with a high applied potential difference between the two electrodes, with the negatively charged cathode producing the cathode rays. He had already deduced that the particles were negatively charged. Firstly, he applied an electric field in the path between anode and cathode and measured the deflections from the straight path. Now he applied a magnetic field across the cathode ray tube by using an external magnetic field. The cathode ray is deflected by the magnetic field. Now he changed the direction of the external magnetic field and found that the beam of electrons is deflected in the opposite direction. From this experiment, he concluded that the electrostatic deflection is the same as the electromagnetic deflection for the cathode rays and he was able to calculate the charge to mass ratio of the electron.

After these three experiments, he deduced that inside the atom there consist of a subatomic particle, originally named ‘corpuscle’, then changed to ‘electron’ which is 1800 times lighter than the mass of hydrogen atom (Lightest atom).

Formula Used

The derivation of the formula used to calculate the charge to the mass ratio:

For Electric Field the force on a particle is

Force(F)=Charge(Q)*Electric field(E) ---<1>

For Magnetic Field the force on a particle moving with velocity is:

F=q*velocity(v)*Magnetic Field(B) ---<2>

From 1 and 2 we get,

V=E/B ----<3>

From the definition of Force,

Acceleration(a)= Force(f)/mass(m) ----<4>

Combining 1 and 4

a=q*E/m ----<5>

From Newton’s law Of motion, vertical displacement is:

Y= (1/2)*a*t*t ----<6>

From 5 and 6

q/m=(2*y*v*v)/x*x*E

Cathode Ray Tubes (CRT) 

The cathode ray tube (CRT) is a vacuum tube, in which electrons are discharged from the cathode and accelerated through a voltage, and thereby gains acceleration of some 600 km/s for every volt. These accelerated electrons collide into the gas inside the tube, thereby allowing it to glow. This enables us to see the path of the beam. Helmholtz coil, a device for producing a region of nearly uniform magnetic field, is also used to apply a quantifiable magnetic field by passing a current through them.

A magnetic field will cause a force to act on the electrons which are perpendicular to both the magnetic field and their direction of travel. Thus, a circular path will be followed by a charged particle in a magnetic field. The faster the speed of a charged particle in a magnetic field, the larger the circle traced out in a magnetic field. Contrarily, the larger the magnetic field needed for a given radius of curvature of the beam. The paths of the electrons are distorted by the magnet in CRT Tv when they are brought near the screen. The picture on the screen appears when the electrons accurately hit phosphors on the back of the screen. Because of this, different colors of light are emitted on the screen when the electrons are impacted. Hence, the electrons are forced to settle in the wrong place, thereby causing the distortion of the image and the psychedelic colors.

Postulates of J.J. Thomson’s Atomic Model

After the Cathode ray tube experiment, Thomson gave one of the first atomic models including the newly discovered particle. 

His model stated: -

An atom resembles a sphere of positive charge with a negative charge present inside the sphere.

The positive charge and the negative charge were equal in magnitude and thus the atom had no charge as a whole and is electrically neutral.

His model resembles a plum pudding or watermelon. It assumed that positive and negative charge inside an atom is randomly spread across the whole sphere like the red part of the watermelon (positive charge) and the black seeds (negative charge).

Practical Uses of Cathode Ray Tube Experiment

In ancient times, the cathode ray tubes were used in the beam where the electron was considered with no inertia but have higher frequencies and can be made visible for a short time.

Many scientists were trying to get the secrets of cathode rays, while others were in search of the practical uses or applications of cathode ray tube experiments. And the first search was ended and released in 1897 which was introduced as Karl Ferdinand Braun’s oscilloscope. It was used for producing luminescence on a chemical affected screen in which cathode rays were allowed to pass through the narrow aperture by focusing into the beams that looked like a dot. This dot was passed for scanning across the screen which was represented visually by the electrical pulse generator. 

Then during the first two to three decades of the twentieth century, inventors continued to search the uses of cathode ray tube technology. Then inspired by Braun's oscilloscope, A. A. Campbell advised that a cathode ray tube would be used for projecting video images on the screen. But, this technology of the time did not get matched with the vision of Campbell-Swinton. It was only until 1922, when Philo T. Farnsworth developed a magnet to get focused on the stream of electrons on the screen, for producing the image. Thus, the first kind of it, Farnsworth, was quickly backed up by Zworykin’s kinescope, known as the ancestor of modern TV sets.

Nowadays, most image viewer devices are made with the help of cathode ray tube technology including the guns of electrons which are used in huge areas of science as well as medical applications. One such use for cathode-ray tube research is the microscope invented by Ernst Ruska in 1928. The microscope based on electrons uses the stream of electrons to magnify the image as the electrons have a small wavelength which is used for magnifying the objects which are very small to get resolved by visible light. Just like Plucker and Crookes work, Ernst Ruska used a strong field of magnetic lines for getting it focused on the stream of electrons into an image.

Solved Example:  

Question: The charge of an electron e=1.602∗10−19 and its is mass m=9.11∗10−31. The stopping potential of an electron traveling in a cathode ray tube is V=5V. Find the velocity of an electron traveling (where charge of an electron e=1.602∗10−19 and mass m=9.11810−31).

Answer: Here we need to find the velocity of traveling electrons using the given stopping potential.

We know that eV=12mv2, the charge(e) and mass(m) of the electron is also given as,

e=1.602∗10−19 and m=9.11∗10−31

By substituting the values of e, m, V.(1.602∗10−19)(5)

=12(9.11∗10−31)(v2)v2

=(1.602∗10−19)(5)(2)9.11∗10−31v

=1.33∗106m/s             

FAQs on Cathode Ray Experiment

1. What is the procedure of the Cathode Ray Experiment?

The apparatus of Cathode Ray Experiment is arranged in such a way that the terminals have high voltage with the internal pressure, which is reduced by removing the air inside the CRT. Because of the high voltage in the terminal,  the partial air inside it is ionized and hence gas becomes the conductor. The electric current propagates as a closed-loop circuit. In order to recognize and measure the ray produced, a dipole is set up. The cathode rays will begin deflecting and repel from the dipole and move towards the anode because of the dipole. The phosphorescent substance is arranged in such a way that the rays strike the substance. And hence, it causes small sparks of light, which detects the stream of rays.

2. What are Cathode ray tubes?

Cathode ray tubes (CRT) are a presentation screen that produces pictures as a video signal. Cathode ray tubes (CRT) is a type of vacuum tube that displays pictures when electron beams from an electron gun hit a luminous surface. The CRT produces electron beams, accelerates them at high speed, and thereby deflecting them to take pictures on a phosphor screen. Electronic presentation gadgets being the most established and least expensive electronic presentation innovation, were initially made with CRTs. CRTs work at any aspect ratio, at any resolution, and geometry without the need to resize the picture. CRTs work on the principle of an optical and electromagnetic phenomenon, called cathodoluminescence.

3. What are the applications of Cathode ray tubes?

The following are the applications of Cathode ray tubes.

The main components of a cathode ray tube (CRT) includes A Vacuum tube holding an electron cannon and a screen lined with phosphors.

The technology of Cathode ray tubes is used by Televisions and computer monitors. Three electron cannons correlate to corresponding types of phosphors in color CRTs, one for each main color viz red, green, and blue.

Ancient computer terminals and black and white televisions are examples of monochromatic CRTs.

cathode ray tube (CRT) is also used in oscilloscopes, which are machines that display and analyze the waveform of electronic signals.

A cathode ray amusement device was the very first video game to be produced, which were used in old military radar screens.

4. What are the basic principles of the CRT?

There are three basic principles of the CRT as the following:

Electrons are released into a vacuum tube from very hot metal plates.

The released electrons are accelerated and their direction of movement is controlled by using either a magnetic field from a coil that is carrying an electric current or by a voltage between metal plates.

A high-velocity beam of electrons hits some materials such as zinc sulfide. The spot is created on the fluorescent screen, and it causes material, called a phosphor, to glow, giving a spot of light as wide as the beam.

5.  How to understand the concept of the Cathode Ray Experiment easily?

Students can understand the concept of the Cathode Ray Experiment easily with the help of a detailed explanation of the Cathode Ray Experiment provided on Vedantu. Vedantu has provided here a thorough explanation of the Cathode Ray Experiment along with Cathode Rays, How Do the Cathode Rays Work, Construction of a Cathode Ray Tube, Postulates of J.J. Thomson’s Atomic Model, and Practical Uses of Cathode Ray Tube Experiment along with examples. Students can learn the concepts of all the important topics of Science subject on Vedantu.

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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.

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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

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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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