JEE Main Physics - Electronic Devices
Exam Duration: 60 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
In sample of pure silicon 1023 e/m3 is mixed to phosphorous. If all atoms are active, then what will be the resistivity at 20oC, if mobility of electron is 1200 cm2/V-s?
- (a)
0.5209 ohm-cm
- (b)
5.209 ohm-cm
- (c)
52.09 ohm-cm
- (d)
520.9 ohm-cm
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
The current gain of a transistor in a common emitter configuration is 40. If the emitter current is 8.2 mA, then base current is
- (a)
0.02 mA
- (b)
0.2 mA
- (c)
2.0 mA
- (d)
0.4 mA
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
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)
Carbon, silicon and germanium have four valence electrons each. At room temperature, which one of the following statement is most appropriate?
- (a)
The number of free conduction electrons is significant in C but small in Si and Ge
- (b)
The number of free conduction electrons is negligibly small in all three
- (c)
The number of free electrons for conduction is significant in all the three
- (d)
The number of free electrons for conduction is significant only in Si and Ge but small in C
In a common-base mode of a transistor, the collector current is 5.60 mA. The value of the base current amplification factor \((\beta)\) will be,
- (a)
49
- (b)
50
- (c)
51
- (d)
48
In the following, which one of the diodes is reverse biased?
- (a)
- (b)
- (c)
- (d)
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)
\(\pi/2\)
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