10 QA on thermionic tubes

10 QA on thermionic tubes | Learn Physics

10 Question-answer on thermionic tubes

1. In metals:

(a) All the electrons are free

(b) There is not a single free electron

(d) There is a large number of free electrons.

Ans: (d)

2. From the surface of metal, the free electrons cannot come out because

(a) Atoms of metal become negative

(b) Other electrons repel

(d) It experiences attraction with other electrons.

Ans: ( c)

3. The energy needed for electron to become free from the surface of metal with zero velocity is called as

(a) Kinetic energy

(b) Potential energy

(d) Work function

Ans: (d)

4. Work function of metal depends upon

(a) Its mass

(b) Its valency

(d) None of the above

Ans: (c)

5. The maximum possible energy of electron in a metal at absolute zero temperature is said to be:

(a) Potential energy

(b) Kinetic energy

(d) Binding energy

Ans: ( c)

6. Emission of electrons by heating metals is said to be

(a) Thermionic emission

(b) Photoelectric emission

(d) Secondary emission

Ans: (a)

7. The phenomenon of thermionic emission was discovered by

(a) Marconi

(b) Fleming

(d) Thomas Edison

Ans: (d)

8. Thermionic process does not depend upon

(a) Work function

(b) Surface area

(d) Melting point

Ans: (d)

9. The number of thermionic electrons emitted by a cathode does not depend on

(a) Its specific heat capacity

(b) Temperature of cathode

(d) Work function of metal of cathode.

Ans: (a)

10. The value of thermionic current density for two metals of equal area and temperature will be

(a) Less for metal of less work function

(b) More for metal of less work function

(d) Independent of work function

Ans: (b)

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