Semiconductors(11th And 12th > Physics ) Questions and answers for exam Preparation

11th And 12th > Physics

SEMICONDUCTORS MCQs

Total Questions : 30 | Page 3 of 3 pages

Question 21.

How many NAND gates are used in an OR gate?

Four
Two
Three
Five

Discuss Question

Answer: Option C. -> Three
:
C

For this purpose we use three NAND gate in manner as shown. The first two NAND gates are operated as NOT gates and their outputs are fed to the third. The resulting circuit is OR gate.

Question 22.

A p-n junction (D) shown in the figure can act as a rectifier. An alternating current source (V) is connected in the circuit. The current (I) in the resistor (R) can be shown by

Discuss Question

Answer: Option B. -> b
:
B

The given circuit works is half wave rectifier. In this circuit, we will get current through R when p-n junction diode is forward biased and no current when p-n junction is reversed biased. Thus the current through resistance will be shown by graph (b).

Question 23.

To get an output Y = 1 from the circuit shown in figure the inputs A, B and C must be respectively

1, 0, 1
1, 1, 0
0, 1, 0
1, 0, 0

Discuss Question

Answer: Option A. -> 1, 0, 1
:
A

The output of OR gate is

Y’ = (A + B)

The output and AND gate is

Y = Y’ . C = (A + B) . C

If A = 1, B = 0, C = 1, they Y = (1 + 0). 1 = 1

Question 24.

In an unbiased p-n junction,

potential at p is equal to that at n
potential at p is +ve and that at n is –ve
potential at p is more than that at n
potential at p is less than that at n

Discuss Question

Answer: Option D. -> potential at p is less than that at n
:
D

Option (d)
At the barrier, there are electron concentration on p side.

Question 25.

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.

Question 26.

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 27.

In common base mode of transistor, the collector current is 5.488 mA for an emitter current of 5.60 mA. The value of the base current amplification factor $(β)$ will be

48
49
50
51
35 mA

Discuss Question

Answer: Option B. -> 49
:
B

$I_{b} = I_{e} - I_{c}$ = 5.60 - 5.488 = 0.112 mA
$β = \frac{I_{e}}{I_{b}} = \frac{5.488}{0.112}$ = 49.

Question 28.

In the circuit as shown in figure, A and B represent two inputs and C represents the

OR gate
NOR gate
AND gate
NAND gate
35 mA

Discuss Question

Answer: Option A. -> OR gate
:
A

The circuit represents OR gate, as the output at C is 1, when either A or B or both A and B have input at level 1. But output at C is zero, when both A and B are at zero level and the Boolean expression is C = (A + B).

Question 29.

The current I through 10 $Ω$ resistor in the circuit shown in figure.

50 mA
20 mA
40 mA
80 mA
35 mA

Discuss Question

Answer: Option D. -> 80 mA
:
D

In the given circuit, junction diode $D_{1}$ if forward biased, will conduct current and junction diode $D_{2}$ is reverse biased, will not conduct current. Therefore, current
I = $\frac{2}{10 + 15}$ = 0.08 A = 80 mA.

Question 30.

A working transistor with its three legs marked P, Q and R is tested using a multi-meter. No conduction is found between P and Q. By connecting the common (negative) terminal of the multimeter to R and the other (positive) terminal to P or Q, some resistance is seen on the multi-meter. Which of the following is true for the transistor?

It is an n-p-n transistor with R as collector
It is an n-p-n transistor with R as base
It is an p-n-p transistor with R as collector
It is an p-n-p transistor with R as emitter
35 mA

Discuss Question

Answer: Option B. -> It is an n-p-n transistor with R as base
:
B

When a multimeter is connected between P and Q there is no conduction between P and Q, then P and Q are of same type of semiconductor, ie, either both are on n-type or of p-type. It means emitter and collector of a transistor are P and Q. When R is connected to negative terminal of multimeter and positive terminal to P or Q, then emitter-base junction will conduct to some extent due to reverse biasing.

The similar is the case of collector – base junction. Thus the transistor is n-p-n transistor with R as base.