## JEE Main Previous Year Papers Questions With Solutions Physics  Semiconductor Devices

Multiple Choice with ONE correct answer

Ans.

2.The probability of electrons to be found in the conduction band of an intrinsic semiconductor at a finite temperature [1995]
a) increases exponentially with increasing band  gap
b) decreases exponentially with increasing ban  gap
c) decreases with increasing temperature
d) is independent of the temperature and the band  gap
Ans.

3.A full wave rectifier circuit along with the output is shown in figure. The contribution(s) from the diode 1 is (are) [1996-2 marks]

Ans.(c)As given in the figure, diode (1) is reverse biased in first half cycle and hence non ­conducting.

During the second half cycle, diobe (1) is forward biased and hence conducting.Thus diode (1) conducts only in a alternate half cycles. The contributions from the diode (1) are B and D.

4.The electrical conductivity of a semiconductor increases when electromagnetic radiation of wavelength shorter than 2480 nm is incident on it. The badn gap (in eV) for the semiconductor is[1997-1 mark]
a) 0.9   b) 0.7    c) 0.5    d) 1.1

Ans.

5.The dominant mechanisms for motion of charge  carriers in forward and reverse biased silicon p-n junctions are [1997-1 mark]
a) drift in forward bias, diffusion in reverse bias
b) diffusion in forward bias, drift in reverse bias
c) diffusion in both forward and reverse bias
d) drift in both forward and reverse bias.

Ans.(b) Drift current flows form pâ€” side to n â€” side.Diffusion current flows from n â€” side to p – side. In forward biasing, drift current is greater than the diffusion current.In reverse biasing, the diffusion current is greater than the drift current.Option (b) represents the answer.

6.The circuit shown in the figure contains two diodes  each with a forward resistance of 50 ohm and with infinite backward resistance. If the battery voltage is 6 V, the current through the 100 ohm resistance (in ampere)is [1997-1 mark]
a) zero    b) 0.02    c) 0.03   d) 0.036

Ans.

7.Which of the following statements is not true?
a) The resistance of intrinsic semiconductor decreases with increase of temperature
b) Doping pure Si with trivalent impurties gives p -type semiconductors
c) The majority carriers in n-type semiconductors are holes
d) A p-n junction can act as a semiconductor diode.[1997-1 mark]

Ans.(c) Statement (c) is not true.The majority carriers in nâ€” type semiconductors are electrons, not holes.

Multiple Choice with ONE or  More Than ONE correct answers

8.Select the correct statement from the following:  [1984 – 2 Marks]
a) A diode can be used as a rectifier
b) A triode cannot be used as a rectifier
c) The current in a diode is always proportional to the applied voltage
d) The linear portion of the I- V characteristic of a triode is used for amplification without distortion.

Ans.(a)A diode can be used as a rectifier.  Option (a) is correct  Other options are not correct.

9.For a given plate voltage, the plate current in a triode value is maximum when the potential of
[1985-2 marks]
a) the grid is positive and plate is negative
b) the grid is zero and plate is positive
c) the grid is negative and plate is positive
d) the grid is positive and plate is positive.IIT

Ans.For maximum plate current in a triode value is available, for a given plate voltage, when grid is positive and plate is positive.

10.The impurity atoms, with which pure silicon should  be doped to make a p -type semiconductor, are those of [1988-2 marks]
a) phosphorus       b) boron
c) antimony           d) aluminium.

Ans.(b), (d) p â€” type semiconductor is obtained when Si or Ge (tetravalent) is doped with group III trivalent impurities like aluminium, boron etc.

11.Two identical p â€” n junctions may be connected in series with a battery in three ways, as shown in figure. The potential drops across the two p â€” n junctions are equal in [1989-2 makrs]

a)circuit 1 and circuit 2
b) circuit 2 and circuit 3
c) circuit 3 and circuit 1
d) circuit 1 only

Ans.The potential drops across the two p â€” ti junctions, connected in series, are equal in circuit 2 and circuit 3. These two circuits are either forward biased or reverse biased in terms of the p â€” n junctions.

12.In an n â€” p â€” n transistor circuit, the collector  current is 10 mA. If 90% of the electrons emitted reach the collector, [1992-2 marks]
a) the emitter current will be 9 mA
b) the base current will be 1 mA
c) the emitter current will be 11 mA
d) the base current will be -1 mA.

Ans.

13.Holes are charge carrier in [1996-2 marks]
a) intrinsic semiconductors     b) ionic solids
c) p â€” type semiconductors     d) metals

Ans.(a), (c) In intrinsic semiconductor, nh â€” ne In p â€” type semiconductor , nh > ne

14.A transistor is used in the common emitter mode  as an amplifier. Then [1998-2 marks]
a) the base-emitter junction is forward-biased.
b) the base-emitter junction is reverse-biased.
c) the input signal is connected in series with the voltage applied to bias the base-emitter junction.
d) the input signal is connected in series with the voltage applied to bias the base-collector junction.

Ans.(a), (c) When a transistor is used in the common emitter mode as an amplifier, then the options (a) and (c) are correct.

15.In a p â€” n junction diode, not connected to any  circuit, [1998-2 marks]
a) the potential is the same every where
b) the stype side is at a higher potential than the n â€” type side.
c) there is an electric field at the junction directed from the n â€” type side to the p â€” type side.
d) there is an electric field at the junction directed fromt he p â€” type side to the n â€” type side.

Ans.(c) In a p â€” n junction diode, a depletion layer or a potenial barrier is formed.  The nâ€” side of depletion layer is at higher potential; and p â€” side is at lower potential.

Subjective / Numerical integer type
16.A triode has plate characteristics in the form of parallel lines in the region of our interest. At a grid voltage of -1 volt the anode current / (in milli ampere) is given in terms of plate voltage V(in volt) by the algebraic relation:
I = 0.125V-7.5 .
For grid voltage of -3 volt, the current at anode voltage of 300 volt is 5 milliampere. Determine the plate resistance (rp), transconductance (gm) and the amplification factor ( )for the triode.[1987-7 marks]

Ans.

True / False Type
17.For a diode the variation of its anode current Ia  with the anode voltage Va at two different cathode temperatures T1 and T2 is shown in the figure. The temperature T2 is greater than T1. [1986- 3 marks]

Ans.TRUE : With increase in cathode temperature, the number of electrons emitted from cathode increases. Consequently the anode current increases

Fill in the blanks
18.In the forward bias arrangement of a p-n junction  rectifier, the p end is connected to the……. terminal
of the battery and the direction of the current is from……. to……… in the rectifier.  [1988-2 marks]

Ans.The p -end is connected to positive terminal. Direction of current is from p to

19…………..biasing of p-n junction offers high resistance  to current flow across the junction. The biasing is obtained by connecting the p- side to the……… terminal of the battery. [1990-2 marks]
Ans.Reverse biasing is obtained when pâ€” side is connected to the negative terminal of battery.

20.For the given circuit shown in fig. to act as full wave rectifier, the a.c. input should be connected  across …………….and……….. and the d.c. output would  appear across…………. and…………….. [1991-1 mark]

Ans.B  and D: for a.c.input
A and C: for d.c. output

21.In a………….. biased p-n junction, the net flow of holes  is from the n region to the p region.[1993 -1 mark]
Ans.The given property is related with reverse biased p â€” n