Material Science (Semiconductor Physics)
1. The total energy of a revolving electron in an atom can
(a) have any value above zero
(b) never be positive
(c) never be negative
2. An atom is said to be ionised when any one of its orbiting electron
(a) Jumps from one orbit to another
(b) is raised to a higher orbit
(c) comes to the ground state
(d) is completely removed.
3. The maximum number of electrons which the Mshell
of an atom can contain is
(a) 32
(b) 8
(c) 18
(d) 50.
4. Electronic distribution of an Si atom is
(a) 2, 10, 2
(b) 2, 8, 4
(c) 2, 7, 5
(d) 2, 4, 8.
5. Semiconductor materials have ................. bonds.
(a) ionic
(b) covalent
(c) mutual
(d) metallic.
6. The maximum number of electrons which the valence shell of an atom can have is
(a) 6
(b) 8
(c) 18
(d) 2
7. Silicon has Z = 14. Its outermost orbit is
(a) partially filled
(b) half filled
(c) completely occupied
(d) empty
8. Major part of the current in an intrinsic semiconductor is due to
(a) conductionband
electrons
(b) valenceband
electrons
(c) holes in the valence band
(d) thermallygenerated
electron.
9. Conduction electrons have more mobility than holes because they
(a) are lighter
(b) experience collisions less frequently
(c) have negative charge
(d) need less energy to move them.
10. Doping materials are called impurities because they
(a) decrease the number of charge carriers
(b) change the chemical properties of semiconductors
(c) make semiconductors less than 100 percent pure
(d) alter the crystal structures of the pure semiconductors.
11. Current flow in a semiconductor depends on the phenomenon of
(a) drift
(b) diffusion
(c) recombination
(d) all of the above.
12. The process of adding impurities to a pure semiconductor
is called
(a) mixing
(b) doping
(c) diffusing
(d) refining.
13. The most widely used semiconducting material in electronic devices is
(a) germanium
(b) silicon
(c) copper
(d) carbon
14. Electronhole
pairs are produced by
(a) recombination
(b) thermal energy
(c) ionization
(d) doping
15. Recombination takes place when
(a) an electron falls into a hole
(b) a positive and a negative ion bond together
(c) a valence electron becomes a conduction
(d) a crystal is formed
16. When a PN
junction is formed, diffusion current causes
(a) mixing of current carriers
(b) forward bias
(c) reverse bias
(d) barrier potential.
17. The leakage current of a PN
diode is caused by
(a) heat energy
(b) chemical energy
(c) barrier potential
(d) majority carriers.
18. Electronic components which are made of a semiconductor material are often called
................... devices.
(a) solidstate
(b) silicon
(c) germanium
(d) intrinsic.
19. Any voltage that is connected across a PN
junction is called ............. voltage.
(a) breakdown
(b) barrier
(c) bias
(d) reverse.
20. The area within a semiconductor diode where no mobile current carriers exist when it
is
formed is called .......... region.
(a) depletion
(b) saturation
(c) potential barrier
(d) space charge.
21. The depletion region of a semiconductor diode is due to
(a) reverse biasing
(b) forward biasing
(c) crystal doping
(d) migration of mobile charge carriers.
22. If an intrinsic semiconductor is doped with a very small amount of boron, then in the
extrinsic semiconductor so formed, the number of electrons and holes will,
(a) decrease
(b) increase and decrease respectively
(c) increase
(d) decrease and increase respectively.
23. Two initially identical samples A and B of pure germanium are doped with donors to
concentrations of 1 × 1020 and 3 × 1020 respectively. If the hole concentration in A is 9 ×
1012, then the hole concentration in B at the same temperature will be
(a) 3 1012 m3
(b) 7 × 1012 m3
(c) 11 × 1012 m3
(d) 27 × 1012 m3
24. Hall effect is observed in a specimen when it (metal or a semiconductor) is carrying
current and is placed in a magnetic field. The resultant electric field inside the specimen
will be in
(a) a direction normal to both current and magnetic field
(b) the direction of current
(c) a direction anti parallel to the magnetic field
(d) an arbitrary direction depending upon the conductivity of the specimen.
Answers:
1. (b) 2. (d) 3. (c) 4. (b) 5. (b) 6. (b) 7. (b) 8. (a) 9. (d) 10. (d) 11. (d) 12. (b) 13. (b) 14. (b)
15. (a) 16. (d) 17. (a) 18. (a) 19. (c) 20. (a) 21. (d) 22. (d) 23. (a) 24. (a)
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