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Thermionic emmision |
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The release of electrons from the heated metal surface. |
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The factor that influences thermionic emission:
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- The temperature of the cathode
- As the temperature of the cathode increases, the rate of thermionic emission increases.
- The surface area of the cathode
- As the surface area of the cathode increases, the rate of thermionic emission increases.
- The potential difference between anode and cathode
- As the potential difference between the anode and the cathode increases, the electron velocity increases, causing the electron beam to accelerate.
- The type of cathode
- Cathode plating
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The characteristics of cathode rays:
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- Move-in a straight line at high velocity.
- Has momentum and kinetic energy.
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Kinetic energy \(\rightarrow\) light energy when an electron hits a fluorescent screen.
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Produces X-rays when exposed to heavy metals.
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Charged –ve.
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Can be deflected by magnetic field (Fleming left hand).
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