Semiconductors(12th Grade > Physics ) Questions and answers for exam Preparation

12th Grade > Physics

SEMICONDUCTORS MCQs

Total Questions : 30 | Page 2 of 3 pages

Question 11. The combination of the following gates produces

AND gate
NAND gate
NOR gate
OR gate

Discuss Question

Answer: Option A. -> AND gate
:
A
Output of first NAND gate is,

Y^{'} = ¯ ¯¯¯¯¯¯¯¯¯ ¯ A . B

Output of second NAND gate is,

Y = {¯ ¯¯ ¯ Y}^{'} = ¯ ¯¯¯¯¯¯¯¯¯ ¯ ¯ ¯¯¯¯¯¯¯¯¯ ¯ A . B = A . B

Thus AND gate is formed.

Question 12. Diode valve is discovered by

Richardson
Dushman
Edison
Fleming

Discuss Question

Answer: Option D. -> Fleming
:
D
Diode valve is discovered by Fleming.

Question 13. The value of current in the following diagram will be

zero
10−2 A
10 A
0.025 A

Discuss Question

Answer: Option B. -> 10−2 A
:
B
Here p-n junction as forward biased with voltage
= 5 - 3 = 2 V.

∴

Current

I = \frac{2}{200} = \frac{1}{100} = 10^{- 2} A

Question 14. When the electrical conductivity of a semiconductor is only due to the breaking of its covalent bonds, then the semiconductor is said to be

Donor
Acceptor
Intrinsic
Extrinsic

Discuss Question

Answer: Option C. -> Intrinsic
:
C
In the case of semiconductors, electron-hole pairs are generated only due to the breaking of covalent bonds. There is no other source of generation of electron-hole pairs. Hence when the electrical conductivity of a semiconductor is only due to the breaking of its covalent bonds, then the semiconductor is said to be an intrinsic semiconductor.

Question 15. Two identical p-n junction may be connected in series with a battery in three ways as shown in the adjoining figure. The potential drop across the p-n junctions are equal in

circuit 1 and circuit 2
circuit 2 and circuit 3
circuit 3 and circuit 1
circuit 1 only

Discuss Question

Answer: Option B. -> circuit 2 and circuit 3
:
B
In circuit 1, N is connected with N, which is not a series combination of p-n junction. In circuit 2, each p-n junction is forward biased, hence same current flows, giving same potential difference across p-n junction. In circuit 2, each p-n junction is reverse biased; same leakage current will flow, giving equal potential difference across each p-n junction diode.

Question 16. In a PN-junction diode

The current in the reverse biased condition is generally very small
The current in the reverse biased condition is small but the forward biased current is independent of the bias voltage
The reverse biased current is strongly dependent on the applied bias voltage
The forward biased current is very small in comparison to reverse biased current

Discuss Question

Answer: Option A. -> The current in the reverse biased condition is generally very small
:
A
In forward biasedPN-junction, external voltage decreases the potential barrier, so current is maximum. While in reversed biasedPN-junction, external voltage increases the potential barrier, so the current is very small.

Question 17. An n-type semiconductor is

negatively charged
positively charged
neutral
negatively or positively charged depending upon the amount of impurity

Discuss Question

Answer: Option C. -> neutral
:
C
N-type semiconductor is having excess of free electrons (unbound electrons) for conduction. The total number of electrons in an atom is equal to total number of protons in the nucleus. Therefore, n –type semiconductor is neutral.

Question 18. The relation between number of free electrons (n) is a semiconductor and temperature (T) is given by

n α T
n α T2
n α √T
n α T32

Discuss Question

Answer: Option D. -> n α T32
:
D
For semiconductor,

n = A T^{\frac{3}{2}} e^{\frac{- E_{g}}{2 k T}};

So,

n α T^{\frac{3}{2}}

Question 19. The average value of output direct current in a half wave rectifier is

I0π
I02
πI02
2I0π

Discuss Question

Answer: Option A. -> I0π
:
A
The average value of output direct current in a half wave rectifier is
=

\frac{(average value of current over a cycle)}{2}

\frac{(\frac{2 I_{0}}{π})}{2} = \frac{I_{0}}{π}

Question 20. A Si and a Ge diode has identical physical dimensions. The band gap in Si is larger than that in Ge. An identical reverse bias is applied across the diodes

The reverse current in Ge is larger than that in Si
The reverse current in Si is larger than that in Ge
The reverse current is identical in the two diodes
The relative magnitude of the reverse currents cannot be determined from the given data only

Discuss Question

Answer: Option C. -> The reverse current is identical in the two diodes
:
C
When a diode is reverse biased, then the applied voltage supports the barrier voltage. Due to it, the reverse current is weak. It will be identical in two diodes.