# Physics class 12 chapter 14 Objective Questions

## Semiconductor Electronics

1. Region without free electrons and holes in a p-n junction is

(a) n-region

(b) p-region

(c) depletion region

(d) none of these

1. Which of the following statements is incorrect for the depletion region of a diode?

(a) There the mobile charges exist.

(b) Equal number of holes and electrons exist, making the region neutral.

(c) Recombination of holes and electrons has taken place.

(d) None of these

Answer: (a) There the mobile charges exist.

1. Potential barrier developed in a junction diode opposes the flow of

(a) minority carrier in both regions only

(b) majority carriers only

(c) electrons in p region

(d) holes in p region

1. The breakdown in a reverse biased p-n junction diode is more likely to occur due to

(a) large velocity of the minority charge carriers if the doping concentration is small

(b) large velocity of the minority charge carriers if the doping concentration is large

(c) strong electric field in a depletion region if the doping concentration is small

(d) none of these

Answer: (b) large velocity of the minority charge carriers if the doping concentration is large

1. What happens during regulation action of a Zener diode?

(a) The current through the series resistance (Rs) changes.

(b) The resistance offered by the Zener changes.

(c) The Zener resistance is constant.

(d) Both (a) and (b)

Answer: (d) Both (a) and (b)

1. A zener diode is specified as having a breakdown voltage of 9.1 V, with a maximum power dissipation of 364 mW. What is the maximum current the diode can handle?

(a) 40 mA

(b) 60 mA

(c) 50 mA

(d) 45 mA

1. In a half wave rectifier circuit operating from 50 Hz mains frequency, the fundamental frequency in the ripple would be

(a) 25 Hz

(b) 50 Hz

(c) 70.7 Hz

(d) 100 Hz

1. Carbon, silicon and germanium have four valence electrons each. These are characterised by valence and conduction bands separated by energy band gap respectively equal to (Eg)c, (Eg)Si and (Eg)Ge. Which of the following statements is true?

(a) (Eg)Si < (Eg)Ge < (Eg)C

(b) (Eg)C < (Eg)Ge < (Eg)Si

(c) (Eg)C < (Eg)Si < (Eg)Ge

(d) (Eg)C = (Eg)Si < (Eg)Ge

Answer: (c) (Eg)C < (Eg)Si < (Eg)Ge

1. If the energy of a photon of sodium light (A = 589 nm) equals the band gap of semiconductor, the minimum energy required to create hole electron pair

(a) 1.1 eV

(b) 2.1 eV

(c) 3.2 eV

(d) 1.5 eV

1. If in a n-type semiconductor when all donor states are filled, then the net charge density in the donor states becomes

(a) 1

(b) > 1

(c) < 1, but not zero

(d) zero

1. At absolute zero, Si acts as a

(a) metal

(b) semiconductor

(c) insulator

(d) none of these

1. In good conducrors of electricity the type of bonding that exist is

(a) Van der Walls

(b) covalent

(c) ionic

(d) metallic

1. The manifestation of band structure in solids is due to

(a) Heisenberg uncertainty priniciple

(b) Pauli’s exclusion principle

(c) Bohr’s correspondence principle

(d) Boltzmann law

1. The probability of electrons to be found in the conduction band of an intrinsic semiconductor of finite temperature

(a) increases exponentially with increasing band gaP

(b) decreases exponentially with increasing band gap

(c) decreases with increasing temperature.

(d) is independent of the temperature and band gap

Answer: (b) decreases exponentially with increasing band gap

1. In an n-type silicon, which of the following statements is true.

(a) Electrons are majority carriers and trivalent atoms are the dopants’

(b) Electrons are minority carriers and pentava- lent atoms are the dopants.

(c) Holes are minority carriers and pentavalent atoms are the dopants.

(d) Holes are majority carriers and trivalent atoms are the dopants.

Answer: (c) Holes are minority carriers and pentavalent atoms are the dopants.

1. If a small amount of antimony is added to germanium crystal

(a) its resistance is increased

(b) it becomes a p-type semiconductor

(c) there will be more free electrons than holes in the semiconductor,

(d) none of these.

Answer: (c) there will be more free electrons than holes in the semiconductor,

1. Semiconductor Electronics Question 19. The dominant mechanism for motion of charge carriers in forward and reverse biased silicon p-n junction are

(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

Answer: (b) diffusion in forward bias, drift in reverse bias

1. In an unbiased p-n junction, holes diffuse from the p-region to n-region because

(a) free electrons in the n-region attract them

(b) they move across the junction by the potential difference

(c) hole concentration in p-region is more as compared to u-region.

(d) all of these

Answer: (c) hole concentration in p-region is more as compared to u-region.

1. For Binary number 10101, the number in decimal representation will be :

(A) 31

(B) 21

(C) 11

(D) 3

1. Who designed the transistor ?

(A) Flemming

(B) Shockley

(C) Bravis

(D) Edison