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9.1.2 Cathode Ray

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Electron Gun

(The electrons released by the cathode are accelerated by the accelerating anode and form a beam of electrons)
  1. If a high positive potential (anode) is placed in front of the heated metal, the emitted electrons will be accelerated and form a beam of electrons.
  2. The device is called an electron gun.
  3. The beam produced is called the cathode ray.

Properties of the cathode ray

The properties of cathode ray can be studied by using the Maltese Cross tube and the Deflection Tube.

Maltese Cross Tube

  1. We can use a Maltese cross tube to investigate the characteristics of cathode ray.
  2. Figure below shows the illustration of a Maltese Cross tube.

Experiment

6V DC Supply: ON

3kV EHT: OFF
The filament glows and emits light.
The light is blocked by the cross and hence a shadow is formed on the screen.

6V DC Supply: ON

3kV EHT: ON
The electrons are accelerated by the anode and hence produces a cathode ray.
The cathode ray hit on the screen cause a fluorescent effect.
The cathode ray is also blcok by the cross. Therefore, a shadow form on the screen.

6V DC Supply: ON

3kV EHT: OFF

with Magnet
The cathode ray can be deflected by the magnetic field.
The direction of deflection can be determined by Fleming's Left Hand Rule. (Note: The direction of current is in the opposite direction of electrons movement).

6V DC Supply: ON

3kV EHT: OFF

with Electric Plate
The cathode can be deflected by an electric field.

Deflection Tube


The characteristics of cathode ray can also be determined by using a refflection tube.

Conclusion

  1. Both the experiment of Maltese Cross Tube and the Deflection Tube show that
    1. Cathode ray can produce fluorescent effect.
    2. Cathode ray can be deflected by the electric field.
    3. Cathode ray can be deflected by the magnetic field. The direction of deflection can be determined by using Fleming’s Left hand Rule.