Properties of Cathode Rays

Properties of cathode rays

The properties of cathode rays can be studied using apparatus such as the maltese cross tube and cathode ray deflection tube.

Maltese cross tube

The maltese cross tube has a glass bulb and a hot cathode and an anode enclosed in it. The anode has a hole in the centre so that electrons can pass through it anc shoot across the vacuum. In the middle of the bulb is a second anode in the shape of a Maltese cross. At the end of the tube, there is a fluorescent screen.

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The streams of electrons which leave the cathode and shoot across the vacuum are called cathode rays. The edges of the shadow of the Maltese cross on the screen are sharp. This is because the electrons are travelling in straight lines. Invisible cathode rays travelling across the tube, cast a shadow of the cross on the screen. When electrons strike the screen, the fluorescent screen will glow and light is emitted.

The beam of electrons can be moved by a magnetic field.

Deflection tube

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The properties of a beam of electrons in an electric field can be investigated using a deflection tube as shown above. The cathode is connected to about 6 V AC power supply (AC: Alternating current). The electron gun produces a narrow beam of electrons.

The vertical screen is coated with fluorescent material which will glow when electrons strike it. It can show the path of the beam. There are two horizontal metal plates one above the other. When a voltage is applied accross the metal plates the electron beam will be deflected towards the positive plate.