Cathode rays and cathode ray tube
Cathode-Ray Tubes. Cathode rays are streams of electrons in a vacuum. Each electron conforms very closely to Newtons laws of motion; that is to say, so long as it is not acted upon by any force it stays where it is or moves at constant speed in a straight line, and when a force acts on it in any direction it accelerates in that direction at a rate proportional to the force. An electron is so light that the force of gravity on it is negligible, but it responds smartly to electric and magnetic fields. An electric field is usually measured in volts per metre or cm , and an electron placed in such a field accelerates positive-wards along the imaginary lines of electric force.
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cathode ray
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 on a fluorescent screen to form images. The eminent physicist, Johann Hittorf discovered cathode rays in 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 , the English physicist J. The earliest version of the cathode ray tube, Braun Tube, was invented in 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. Thomson, which employed only electrostatic deflection using two internal plates.
In , 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. This type of cathode consists of a thin filament heated to a very high temperature by passing 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 by the company Telefunken in Germany.
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 0 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 itself 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.
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. It is given a coating of zinc sulphide 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 in every second, that the viewer cannot follow the actual movement of the dot, but can see the whole image so produced. 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. Thomson devised an experiment to test the exact nature. 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 travelled 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.
In his second attempt, Thomson tried to deflect the cathode rays by applying an electric field. It could prove the nature of charge carried by them. There had been attempts before towards achieving the end, but had failed.
He thought that if the streams are electrically charged, then they should be deflected by electric fields, but 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 tried to calculate the charge to mass ratio of the particles constituting the rays and found it to be exceptionally small. That implied the particles to have either a very small mass or 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.
It was highly likely for them to be one of the components of atoms. 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 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. Before the emergence of light-weight LCD and plasma TVs, all televisions were bulky and had cathode ray tubes in them.
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. The predecessor to modern video games, the cathode ray tube amusement device gave world the first gaming device. The CRT produced electronic signals in the form 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 CRT display screen.
The game was conceptualized on World War II missile displays and created an effect of firing missiles at targets. Cathode ray tube monitors are widely used as a display device in radars. However, most CRTs manufactured after , 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 off 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 in 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 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 of hearing. Cathode ray tube was a useful invention in Science for the discovery of an important fundamental particle like electron and also opened up newer arenas of research in atomic Physics.
Until about the year , it was the mainstay of televisions all over the world, before being forced into oblivion due to the emergence of newer technologies. Your email address will not be published. Save my name, email, and website in this browser for the next time I comment.
All rights reserved. Reproduction in whole or in part without permission is prohibited. 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 on a fluorescent screen to form images.
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. Cathode Ray Tube Diagram Deflection System The electron stream, after coming out of the anode, tends to spread out in the form of a cone.
Cathode Ray Tube (CRT)
An old TV set, like the one seen below, is difficult to find these days. The main reason is because these sets are based on outdated technology. The new TV sets are flat screen technology that take up less space and give better picture quality, especially with the advent of high-definition broadcasting. The technology used in the older TV sets used cathode ray tubes. A beam of electrons was sprayed to a picture tube, which was treated to react with the electrons to produce an image.
Rays and Particles
A cathode ray is a beam of electrons in a vacuum tube traveling from the negatively charged electrode cathode at one end to the positively charged electrode anode at the other, across a voltage difference between the electrodes. They are also called electron beams. The electrode at the negative end is called a cathode. The electrode at the positive end is called an anode. Since electrons are repelled by the negative charge, the cathode is seen as the "source" of the cathode ray in the vacuum chamber. Electrons are attracted to the anode and travel in straight lines across the space between the two electrodes. Cathode rays are invisible but their effect is to excite atoms in the glass opposite of the cathode, by the anode. They travel at high speed when voltage is applied to the electrodes and some bypass the anode to strike the glass. This causes atoms in the glass to be raised to a higher energy level, producing a fluorescent glow.
Cathode ray
A cathode ray is a stream of electrons that are seen in vacuum tubes. It is called a "cathode ray" because the electrons are being emitted from the negative charged element in the vacuum tube called the cathode. A cathode ray tube aims the ray at a point on its screen. They were first observed in by German physicist Johann Hittorf , and were named in by Eugen Goldstein Kathodenstrahlen , or cathode rays.
M8-S5: The Electron
Discovering how cathode rays behave in a magnetic field was a big step forward for scientists trying to understand the mysterious phenomenon. Cathode rays were a great mystery throughout the latter half of the nineteenth century. Thomson are just a small sample of the many great minds who contributed to the modern understanding of cathode rays. By the dawn of the twentieth century, their work on the enigmatic rays proved that they are a stream of electrons. Reaching this understanding required many small but important experimental steps to determine, for instance, whether cathode rays travel in straight lines, carry energy or, as explored in this tutorial, are affected by magnetic fields.
Cathode ray facts for kids
Cathode ray tube is an electron tube containing phosphorescence with the help of electron guns and used for taking screenshots. One of the elements required for the control and repair of electronic equipment is the cathode ray tube. What is a cathode ray tube? What is a cathode ray tube used for? What is a cathode ray oscilloscope and how is it used? Let's examine everything about the cathode ray tube together.
4.7: Cathode Ray Tube
From an catalog of demonstration apparatus. Typical cathode ray tube. Thomson, cience lecturers who traveled from town to town in the mid nineteenth century delighted audiences by showing them the ancestor of the neon sign.
What Is A Cathode Ray Tube?
Cathode rays are highly energetic electrons moving from the cathode to the anode. They are produced in a cathode ray tube. Production of cathode rays. The electrons are produced at the cathode by thermionic emission and are accelerated towards the screen by the anode which is connected to the terminal of the extra high tension battery. The thermionic emission is the process whereby metal surfaces emit electrons when heated. The tube is evacuated to avoid electrons interacting with any particle before they reach the screen.
cathode-ray tube
Electric discharges were passed through rarefied gases in the time of Benjamin Franklin - His friend William Watson, an Englishman, remarked: "It was a most delightful spectacle, when the room was darkened, to see the electricity in its passage. Pais page 79 The experimental arrangement was to have two small metal plates inside a glass container from which the air was gradually removed by a pump. The plate connected to the negative side of the electricity supply was called the cathode, that to the positive side the anode. As the pressure was lowered, a spark which fattened into a purplish glowing, writhing snake appeared going from the cathode to the anode. Lowering the pressure further, as Faraday noticed in the 's, a dark space opened up near the cathode, now called the Faraday Dark Space. The big breakthrough came in the 's when Geissler invented a much better mercury pump. In , Hittorf found that in a very good vacuum 0.
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 on a fluorescent screen to form images. The eminent physicist, Johann Hittorf discovered cathode rays in 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.
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