10 Question-answer on thermionic tubes
1. In metals:
(a) All the electrons are free
(b) There is not a single free electron
(c) Free electrons are less
(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
(c) Surface of metal behaves as a potential barrier
(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
(c) Emission energy
(d) Work function
Ans: (d)
4. Work function of metal depends upon
(a) Its mass
(b) Its valency
(c) Electron density
(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
(c) Fermi energy
(d) Binding energy
Ans: ( c)
6. Emission of electrons by heating metals is said to be
(a) Thermionic emission
(b) Photoelectric emission
(c) Field emission
(d) Secondary emission
Ans: (a)
7. The phenomenon of thermionic emission was discovered by
(a) Marconi
(b) Fleming
(c) Forest
(d) Thomas Edison
Ans: (d)
8. Thermionic process does not depend upon
(a) Work function
(b) Surface area
(c) Temperature
(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
(c) Surface area 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
(c) Equal
(d) Independent of work function
Ans: (b)