Semiconductor Electronics- 1 Practice Questions - DPP for NEET

 Page 1


1. (a) With temperature rise conductivity of semiconductors
increases.
2. (b)
3. (b) In insulators, the forbidden energy gap is very large, in
case of semiconductor it is moderate and in conductors
the energy gap is zero.
4. (c) In intrinsic semiconductors, the creation or liberation
of one free electron by the thermal energy creates one
hole. Thus in intrinsic semiconductors 
eh
nn =
5. (b) Both P-type and N-type semiconductors are neutral
because neutral atoms are added during doping.
6. (d) Conductor has positive temperature coefficient of
resistance but semiconductor has negative temperature
coefficient of resistance.
7. (d)
8. (c) At zero Kelvin, there is no thermal agitation and
therefore no electrons from valence band are able to
shift to conduction band.
9. (c) Antimony is a fifth group impurity and is therefore a
donor of electrons.
10. (d) At 0K temperature semiconductor behaves as an
insulator, because at very low temperature electrons
cannot jump from the valence band to conduction band.
11. (b) Formation of energy bands in solids are due to Pauli’s
exclusion principle.
12. ()
13. (a) In conductors valence band and conduction band may
overlaps.
14. (b) With rise in temperature, conductivity of semiconductor
increases while resistance decreases.
15. (a) Because 
()
d
e
i
v
n eA
=
16. (b) In reverse biasing, width of depletion layer increases.
17. (b) Because in case (1) N is connected with N. This is not
a series combination of transistor.
18. (d) Resistance in forward biasing 
10
fr
R »W
and
resistance in reverse biasing
5
4
1
10
10
fr
Rw
Rw
R
R
R
» WÞ=
19. (b) In forward biasing the diffusion current increases and
drift current remains constant so not current is due to
the diffusion.
In reverse biasing diffusion becomes more difficult so
net current (very small) is due to the drift.
20. (a) In a triclinic crystal a ¹ b ¹ c and a ¹ b ¹ g ¹ 90º
21. (a)
22. (a) In figure (1), (2) and (3). P-crystals are more positive
as compared to N-crystals.
23. (a) Wood is non-crystalline and others are crystalleine.
24. (a) Resistance of conductors (Cu) decreases with decrease
in temperature while that of semi-conductors (Ge)
increases with decrease in temperature.
25. (b)
4
3
(180 120)
1.2 10
(15 10) 10
p
p
p
V
r ohm
I
-
D
-
= = =´
D
-´
26. (a)
1 3
3
g
p
m
ohm 10 33 . 5
) 5 . 3 ( ) 0 . 2 (
10 ) 7 15 (
V
I
g
- -
-
´ =
- - -
´ -
=
D
D
=
27. (a) 64 ) 10 33 . 5 ( ) 10 2 . 1 ( g r
3 4
m p
= ´ ´ ´ = ´ = m
-
28. (a) According to law of mass action, 
2
i eh
n nn = . In
intrinsic  semiconductors n
i
 = n
e
 = n
h
 and for P-type
semiconductor n
e
 would be less than n
i
, since n
h
 is
necessarily more than n
i
.
29. (d) Resistivity of semiconductors decreases with
temperature. The atoms of a semiconductor vibrate with
larger amplitudes at higher temperatures there by
increasing its conductivity not resistivity .
30. (c) We cannot measure the potential barrier of a PN-
junction by connecting a sensitive voltmeter across  its
terminals because in the depletion region, there are no
free electrons and holes and in the absence of forward
biasing, PN- junction offers infinite resistance.