Physics - Electronic Devices
Exam Duration: 45 Mins Total Questions : 30
The conductivity of a semiconductor increases with increase in temperature, because
- (a)
number density of free current carriers increases
- (b)
relaxation time increases
- (c)
both number density of carriers and relaxation time increase
- (d)
number density of current carriers increases, relaxation time decreases but effect of decrease relaxation time is much less than increase in number density.
Mobility of electrons in n-type Ge is 5000 cm2 /V-s and conductivity is 5 mho/cm. If the effect of holes is negligible, then impurity concentration will be
- (a)
6.25 x 1015/cm3
- (b)
9.25 x 1014/cm3
- (c)
6 x 1013/cm3
- (d)
9 x 1013/cm3
When a p-n junction diode is reverse biased
- (a)
electrons and holes are attracted towards each other and move towards the depletion region.
- (b)
electrons and hole move away from the junction depletion region.
- (c)
height of the potential barrier decreases.
- (d)
no change in the current takes place.
Ripple factor of half-wave rectifier is
- (a)
1.21
- (b)
1.6
- (c)
1.5
- (d)
1.4
In an n-p-n transistor circuit, the collector current is 10 mA. If 90% of the electrons emitted, reach the collector, the emitter current(IE) and base current (IB) are given by.
- (a)
IE = 1 mA; IB=11 mA
- (b)
IE = 11 mA; IB=1 mA
- (c)
IE = -1 mA; IB=9 mA
- (d)
IE = 9 mA; IB=-1 mA
A transistor has \(\beta = 40\). A change in base current of \(100 \ \mu A\), produce a change in collector current.
- (a)
\(40 \times 100 \ \mu A\)
- (b)
\(100 -40 \ \mu A\)
- (c)
\(40 + 100 \ \mu A\)
- (d)
\(40 \times 100 \ \mu A\)
In a common emitter transistor, amplifier \(\beta\) is 60, R0 is \(5000 \ \Omega\) and internal resistance of a transistor is \(500 \ \Omega\). The voltage amplification of amplifier will be,
- (a)
500
- (b)
460
- (c)
600
- (d)
560
Three amplifier stages, each with a gain of 10 are cascaded. The overall gain is
- (a)
10
- (b)
30
- (c)
1000
- (d)
100
Which of the following statements concerning the depletion zone of an unbiased p-n junction is(are) true?
- (a)
The width of the zone is independent of the densities of the dopants (impurities)
- (b)
The width of the zone is dependent on the densities of the dopants
- (c)
The electric field in the zone is produced by ionized dopant atoms
- (d)
The electric field in the zone is provided by electrons in the conduction band and the holes in the valence band.
The dominant mechanisms for motion of charge carriers in forward and reverse biased silicon p-n junction are
- (a)
drift in forward biased, diffusion in reverse biased
- (b)
diffusion in forward biased, drift in reverse biased
- (c)
diffusion in both forward and reverse biased
- (d)
drift in both forward and reverse biased
If copper and germanium are heated by 50oC from room temperature, then
- (a)
resistance of copper increases while that of germanium decreases
- (b)
resistance of copper decreases while that of germanium increases
- (c)
resistance of both decreases
- (d)
resistance of both increases
Match the categories of semiconductor given in column I with the words given in column I with the words given in column II and select the correct option from the choices given below
| Column I | Column II |
| (A) Intrinsic semiconductor | Si or Ge doped with trivalent impurity |
| (B) p-type semiconductor | Conductivity due to internal charge carriers |
| (C) n-type semiconductor | Si or Ge doped with pentavalent impurity |
- (a)
A-1, B-3, C-2
- (b)
A-1, B-2, C-3
- (c)
A-2, B-3, C-1
- (d)
A-2, B-1, C-3
Th current voltage relation of diode is given by, I=(e1000V/T - 1) mA, where the applied voltage V is in volt and the temperature T is in kelvin. If a student makes an error measuring \(\pm 0.01 \ V\) while measuring the current of 5 mA at 300 K, what will be the error in the value of current in mA?
- (a)
0.2 mA
- (b)
0.02 mA
- (c)
0.5 mA
- (d)
0.05 mA
The I-V characteristic of an LED is
- (a)
- (b)
- (c)
- (d)
In a full-wave rectifier circuit operating from 50 Hz mains frequency, the fundamental frequency in the ripple would be,
- (a)
50 Hz
- (b)
25 Hz
- (c)
100 Hz
- (d)
70.7 Hz
When an n-p-n transistor is used as an amplifier,
- (a)
electrons move from base to collector
- (b)
holes move from emitter to base
- (c)
electrons move from collector to base
- (d)
holes move from base to emitter
For a transistor amplifier in common-emitter configuration for load impedance \(1 \ k \Omega (h_{fe}=50\) and \(h_{oe}=25 \ \ \mu A/V)\) , the current gain is
- (a)
- 5.2
- (b)
- 15.7
- (c)
- 24.8
- (d)
-48.78
When p-n junction diode is forward biased, then
- (a)
the depletion region is reduced and barrier height is increased
- (b)
the depletion region is widened and barrier height is reduced
- (c)
both the depletion region and barrier height are reduced
- (d)
both the depletion region and barrier height are increased
The difference in the variation of resistance with temperature in a metal and a semiconductor arises essentially due to the difference in the
- (a)
crystal structure
- (b)
variation of the number of charge carriers with temperature
- (c)
type of bonding
- (d)
variation of scattering mechanism with temperature
1654060945.png)
1654060942.png)
1653987551.png)
1653987086.png)
1582095229.jpg)
