Q.1. Define stopping potential.

Ans:- The particular value of negative potential at which photoelectric current becomes zero that is known as stopping potential.

Q.2. What is de-Broglie wave ?

Ans:- The wave which is associated with mouable matter particle is known as the de-Broglie wave or matter wave.

Q.3. Why does thermionic emission take place from a metal surface only ?

Ans:- Thermionic emission take place from a metal surface because the metal has free electron. When a metal is heated, its free electrons get sufficient thermal energy and they can overcome surface barrier.

Q.4. Define threshold frequency, work function and stopping potential with reference to photoelecteic effect.

Ans:- (i) Threshold frequency – The minimum value of the frequency of incident radiation below which the photo electric emission stops.

(ii) Work function – It is the minimum amount of energy required to remove an electron from the surface of given metal.

(iii) Stopping potential – The value of the retarding potential at which the pbotoelectric current becomes zero is called cutoff or stopping potential.