Define the following terms as used in thermionic emission

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 (I) Space charge : It is the collection or distribution of electrons which are emitted from the metal surface on a three dimensional region.

(II) Work function : It is the minimum amount of energy required to remove an electron from a solid ( metal surface).

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An electrostatic CRT has parallel deflection plates 1.5 cm long and 6mm apart. The screen is 55cm from the centre of the deflecting plates. The deflecting and accelerating potentials are 150 V and 2.5 kilovolts respectively. Determine the:

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