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 1869 by German physicist Johann Hittorf, and were named in 1876 by Eugen Goldstein Kathodenstrahlen, or cathode rays.

Electrons were discovered as the constituents of cathode rays in 1897 by British physicist J. J. Thomson. He showed the rays were composed of a previously unknown negatively charged particle, which was later called the electron. Cathode ray tubes (CRTs) use a focused beam of electrons deflected by electric or magnetic fields to create the image in a classic television set.

Some properties of cathode rays:

1. They travel in a straight path.
2. They have a negative electric charge
3. They have particle property
4. Magnets can deflect them
5. Charge/mass ratio of the rays is constant
6. They travel from the cathode to the anode
7. Their properties are independent from the electrodes and gas present in the cathode ray tube.
8. Cathode rays can ionize gas
9. The travel more slowly than light
10. They can heat objects that they hit
11. They can penetrate through thin Aluminium plates
12. They can make phosphors glow

Cathode Ray Media

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  A beam of cathode rays in a vacuum tube bent into a circle by a magnetic field generated by a Helmholtz coil. Cathode rays are normally invisible; in this Teltron tube demonstration, enough gas has been left in the tube for the gas atoms to luminesce when struck by the fast-moving electrons.

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  A diagram showing a Crookes tube connected to a high voltage supply. The Maltese cross has no external electrical connection.

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  Glow discharge in a low-pressure tube caused by electric current.

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  Crookes tube. The cathode (negative terminal) is on the right. The anode (positive terminal) is in the base of the tube at bottom.

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  Cathode rays travel from the cathode at the rear of the tube, striking the glass front, making it glow green by fluorescence. A metal cross in the tube casts a shadow, demonstrating that the rays travel in straight lines.

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  A magnet creates a horizontal magnetic field through the neck of the tube, bending the rays up, so the shadow of the cross is higher.

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  When the magnet is reversed, it bends the rays down, so the shadow is lower. The pink glow is caused by cathode rays striking residual gas atoms in the tube.