CBSE Class 12 Physics Semiconductor Electronics Materials Devices and Simple Circuits MCQs Set C

Question. At absolute zero, Si acts as
(a) non metal
(b) metal
(c) insulator
(d) none of these.

Answer : C

Question. For a p-type semiconductor, which of the following statements is true?
(a) Electrons are the majority carriers and pentavalent atoms are the dopants.
(b) Electrons are the majority carriers and trivalent atoms are the dopants.
(c) Holes are the majority carriers and trivalent atoms are the dopants.
(d) Holes are the majority carriers and pentavalent atoms are the dopants.

Answer : C

Question. To obtain a p-type germanium semiconductor, it must be doped with
(a) indium
(b) phosphorus
(c) arsenic
(d) antimony.

Answer : A

Question. The barrier potential of a p-n junction depends on
(1) type of semiconductor material
(2) amount of doping
(3) temperature
Which one of the following is correct?
(a) (1) and (2) only
(b) (2) only
(c) (2) and (3) only
(d) (1), (2) and (3)

Answer : D

Question. In a p-n junction diode, change in temperature due to heating
(a) affects only reverse resistance
(b) affects only forward resistance
(c) does not affect resistance of p-n junction
(d) affects the overall V – I characteristics of p-n junction.

Answer : D

Question. In forward biasing of the p-n junction
(a) the positive terminal of the battery is connected to p-side and the depletion region becomes thick.
(b) the positive terminal of the battery is connected to n-side and the depletion region becomes thin.
(c) the positive terminal of the battery is connected to n-side and the depletion region becomes thick.
(d) the positive terminal of the battery is connected to p-side and the depletion region becomes thin.

Answer : D

Question. If a full wave rectifier circuit is operating from 50 Hz mains, the fundamental frequency in the ripple will be
(a) 25 Hz
(b) 50 Hz
(c) 70.7 Hz
(d) 100 Hz

Answer : D

Question. Zener diode is used for
(a) amplification
(b) rectification
(c) stabilisation
(d) producing oscillations in an oscillator.

Answer : C

Question. In a p-n junction photo cell, the value of the photoelectromotive force produced by monochromatic light is proportional to
(a) the barrier voltage at the p-n junction
(b) the intensity of the light falling on the cell
(c) the frequency of the light falling on the cell
(d) the voltage applied at the p-n junction.

Answer : B

Question. The device that can act as a complete electronic circuit is
(a) junction diode
(b) integrated circuit
(c) junction transistor
(d) zener diode.

Answer : B

Question. In semiconductors at a room temperature
(a) the valence band is partially empty and the conduction band is partially filled
(b) the valence band is completely filled and the conduction band is partially filled
(c) the valence band is completely filled
(d) the conduction band is completely empty.

Answer : A

Question. C and Si both have same lattice structure; having 4 bonding electrons in each. However, C is insulator whereas Si is intrinsic semiconductor. This is because
(a) in case of C the valence band is not completely filled at absolute zero temperature
(b) in case of C the conduction band is partly filled even at absolute zero temperature
(c) the four bonding electrons in the case of C lie in the second orbit, whereas in the case of Si they lie in the third
(d) the four bonding electrons in the case of C lie in the third orbit, whereas for Si they lie in the fourth orbit.

Answer : C

Question. When arsenic is added as an impurity to silicon, the resulting material is
(a) n-type conductor
(b) n-type semiconductor
(c) p-type semiconductor
(d) none of these.

Answer : B

Question. Application of a forward bias to a p-n junction
(a) widens the depletion zone
(b) increases the potential difference across the depletion zone
(c) increases the number of donors on the n side
(d) decreases the electric field in the depletion zone.

Answer : D

Question. The cause of the potential barrier in a p-n junction diode is
(a) depletion of negative charges near the junction
(b) concentration of positive charges near the junction
(c) depletion of positive charges near the junction
(d) concentration of positive and negative charges near the junction.

Answer : D

Question. A semiconducting device is connected in a series circuit with a battery and a resistance. A current is found to pass through the circuit. If the polarity of the battery is reversed, the current drops to almost zero. The device may be
(a) a p-type semiconductor
(b) an intrinsic semiconductor
(c) a p-n junction
(d) an n-type semiconductor.

Answer : C

Question. When n type semiconductor is heated
(a) number of electrons increases while that of holes decreases
(b) number of holes increases while that of electrons decreases
(c) number of electrons and holes remain same
(d) number of electrons and holes increases equally.

Answer : D

Question. The increase in the width of the depletion region in a p-n junction diode is due to
(a) forward bias only
(b) reverse bias only
(c) both forward bias and reverse bias
(d) increase in forward current

Answer : B

Question. The band gap in germanium and silicon in ev respectively is
(a) 1.1, 0
(b) 0, 1.1
(c) 1.1, 0.7
(d) 0.7, 1.1

Answer : D

Question. In a npn transistor 10¹⁰ electrons enter the emitter in 10^–6 s. 4% of the electrons are lost in the base. The current transfer ratio will be
(a) 0.98
(b) 0.97
(c) 0.96
(d) 0.94

Answer : C

Assertion-Reason Questions

In the following questions, a statement of Assertion (A) is followed by a statement of Reason (R). Choose the correct answer out of the following choices.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false and R is also false.

Question. Assertion (A): When the temperature of a semiconductor is increased, then its resistance decreases.
Reason (R): The energy gap between valence and conduction bands is very small for semiconductors.
Answer : A

Question. Assertion (A): A p-type semiconductor has negative charge on it.
Reason (R): p-type impurity atom has positive charge carrier (electrons) in it.
Answer : D

Question. Assertion (A): The colour of light emitted by a LED depends on as reverse biasing.
Reason (R): The reverse biasing of p-n junction will lower the width of depletion layer.
Answer : D

Question. Assertion (A): Diamond behaves such as an insulator.
Reason (R): There is a large energy gap between valence band and conduction bond of diamond.
Answer : A

Question. Assertion (A): The electrical conductivity of n-type semiconductor is higher than that of p-type semiconductor at a given temperature and voltage applied.
Reason (R): The mobility of electron is higher than that of hole.
Answer : A