Physics - Electronic Devices
Exam Duration: 45 Mins Total Questions : 30
For pure Ge semiconductor, quantity of electron and hole is 1019 e/m3 . If we doped a donor impurity in it with density 1023 e/m3, then quantity of hole (e/m3) in a semiconductor is
- (a)
1015
- (b)
1019
- (c)
1023
- (d)
1027
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
What will be conductivity of pure silicon crystal at 300 K temperature, if electron-hole pairs per cm3 are 1.072 x 1010, \(\mu_e\) = 1350 cm2/V-s and \(\mu_e\) = 480 cm2/V-s ?
- (a)
3.14 x 10-6 mho/cm
- (b)
3 x 106 mho/cm
- (c)
10-6 mho/cm
- (d)
106 mho/cm
Forbidden energy gap of Ge is 0.75 eV. Maximum wavelength of incident radiation of photon for producing electron-hole pair in germanium semiconductor is
- (a)
4200 Å
- (b)
16500 Å
- (c)
4700 Å
- (d)
4000 Å
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
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
A solid which is not transparent to visible light and whose conductivity increases with temperature is formed by,
- (a)
ionic bonding
- (b)
covalent bonding
- (c)
van der Waals bonding
- (d)
metallic bonding
If the ratio of the concentration of electrons to that of holes in a semiconductor is 7/5 and the ratio of currents is 7/4, then what is the ratio of their drift velocities?
- (a)
\(\frac{5}{8}\)
- (b)
\(\frac{4}{5}\)
- (c)
\(\frac{5}{4}\)
- (d)
\(\frac{4}{7}\)
The electric conductivity of a semiconductor increases when electromagnetic radiation of wavelength shorter than 2480 nm, is incident on it. The band gap in (eV) for the semiconductor is
- (a)
1.1 eV
- (b)
2.5 eV
- (c)
0.5 eV
- (d)
0.7 eV
In a common base amplifier, the phase difference between the input signal voltage and output voltage is
- (a)
\(\pi/4\)
- (b)
\(\pi\)
- (c)
zero
- (d)
\(\pi/2\)
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