physics MCQs - 12th class Chapter 07 Mcqs

1

The potential barrier for a silicon p-n junction is approximately

A

0.3 V

B

0.5 V

C

0.7 V

D

1.0 V

2

In a forward biased p-n junction, the p-side is connected to the

A

negative terminal of the battery

B

positive terminal of the battery

C

ground

D

n-side

3

The resistance offered by a p-n junction when it is forward biased is

A

very high

B

infinite

C

of the order of several mega ohms

D

only a few ohms

4

The conversion of alternating current into direct current is called

A

amplification

B

rectification

C

oscillation

D

inversion

5

A full-wave bridge rectifier uses how many diodes?

A

One

B

Two

C

Three

D

Four

6

Light Emitting Diodes (LEDs) are made from special semi-conductors like

A

Silicon

B

Germanium

C

Gallium Arsenide

D

Copper

7

A photo diode is designed to be operated in

A

forward biased condition

B

reverse biased condition

C

no bias condition

D

saturation

8

In a transistor, the central region is called the

A

emitter

B

collector

C

base

D

junction

9

For normal operation of an n-p-n transistor, the emitter-base junction is

A

reverse biased

B

not biased

C

forward biased

D

larger than the collector

10

The current gain (β) of a transistor is the ratio of

A

Ic / Ie

B

Ie / Ib

C

Ic / Ib

D

Ib / Ic

11

In a common emitter amplifier, the output voltage has a phase shift of

A

0°

B

90°

C

180°

D

270°

12

An operational amplifier has a very high

A

output resistance

B

current drain

C

input resistance

D

common-mode gain

13

The open loop gain of a typical op-amp is of the order of

A

Ten

B

hunred

C

thousand

D

10^5

14

In an inverting amplifier configuration, the input signal is applied to the

A

inverting (-) terminal

B

non-inverting (+) terminal

C

output terminal

D

ground

15

The gain of a non-inverting op-amp amplifier is given by

A

-R2 / R1

B

1 + R2 / R1

C

R1 / R2

D

1 + R1 / R2

16

A logic gate that produces a HIGH output only when all its inputs are HIGH is called

A

OR gate

B

NOT gate

C

AND gate

D

NAND gate

17

A logic gate that produces a HIGH output when any of its inputs is HIGH is called

A

AND gate

B

OR gate

C

XOR gate

D

NAND gate

18

The NOT gate is also known as an

A

inverter

B

buffer

C

adder

D

follower

19

The output of a NAND gate is LOW (0) only when

A

any input is LOW

B

both inputs are LOW

C

any input is HIGH

D

both inputs are HIGH

20

The output of an XOR gate is HIGH (1) when the inputs are

A

the same

B

both 0

C

both 1

D

different

21

The resistance of a reverse biased p-n junction is of the order of

A

few ohms

B

kilo ohms

C

micro ohms

D

several mega ohms

22

In a half-wave rectifier, the diode conducts during

A

the positive half-cycle only

B

the negative half-cycle only

C

both halves of the cycle

D

a portion of both cycles

23

During the negative half cycle in a bridge rectifier, diodes that conduct are

A

D1 and D2

B

D3 and D4

C

D1 and D3

D

D2 and D4

24

A seven-segment display uses an array of seven

A

Photo diodes

B

Transistors

C

LEDs

D

Capacitors

25

A photo diode can turn its current ON and OFF in

A

milliseconds

B

microseconds

C

nano-seconds

D

seconds

26

A photovoltaic cell generates a current proportional to the

A

temperature

B

pressure

C

applied voltage

D

intensity of light

27

In a transistor, which region is very thin and lightly doped?

A

Emitter

B

Base

C

Collector

D

Depletion region

28

The relationship between transistor currents is

A

Ib = Ie + Ic

B

Ic = Ie + Ib

C

Ie = Ib + Ic

D

Ie = Ic - Ib

29

When a transistor is used as a switch, it is in the ON state when the base current is

A

zero

B

small

C

very large

D

negative

30

In an op-amp, the resistance between the output terminal and ground is known as

A

Input Resistance

B

Output Resistance

C

Virtual Resistance

D

Loop Gain

31

The potential drop across a silicon diode when it starts conducting is about

A

0.1 V

B

0.3 V

C

0.5 V

D

0.7 V

32

The current that flows in a reverse biased junction due to minority charge carriers is called

A

forward current

B

saturation current

C

leakage current

D

emitter current

33

The symbolic representation of a p-n junction diode has an arrow head that represents the

A

n-region (cathode)

B

depletion region

C

p-region (anode)

D

direction of electron flow

34

A circuit used to smooth the pulsating DC from a rectifier is known as a

A

filter

B

amplifier

C

chopper

D

clipper

35

A device used to convert changes in light intensity into electric voltage is a

A

Thermistor

B

Microphone

C

Light Dependent Resistor (LDR)

D

Capacitor

36

The output of an XNOR gate is 1 when its inputs are

A

identical

B

different

C

both 0

D

both 1

37

The Boolean expression for a NOR gate is

A

X = A . B

B

X = A + B

C

X = A + B (with a bar over it)

D

X = A . B (with a bar over it)

38

The process of adding impurities to a semiconductor is known as

A

doping

B

biasing

C

rectifying

D

diffusing

39

In a p-type semiconductor, the majority charge carriers are

A

electrons

B

holes

C

ions

D

protons

40

In an n-type semiconductor, the majority charge carriers are

A

electrons

B

holes

C

ions

D

neutrons

41

The characteristic curve of a diode is a plot between

A

voltage and time

B

current and time

C

voltage and current

D

resistance and voltage

42

The colour of light emitted by an LED depends on the

A

forward current

B

reverse bias

C

type of semi-conductor material used

D

size of the diode

43

The common emitter current amplification factor β is given by

A

Ic/Ie

B

Ie/Ic

C

Ic/Ib

D

Ie/Ib

44

The output of a two-input OR gate is 0 only when its

A

both inputs are 0

B

either input is 1

C

both inputs are 1

D

either input is 0

45

A two-input NAND gate with inputs A and B has an output 0 if

A

A is 0

B

B is 0

C

both A and B are zero

D

both A and B are 1

46

The truth table with output 1 for identical inputs (00, 11) and 0 for different inputs (01, 10) is for a

A

XOR gate

B

OR gate

C

AND gate

D

XNOR gate

47

The output of the op-amp used as a night switch energizes the relay when

A

V' > VR

B

V' < VR

C

V' = VR

D

V' = 0

48

In digital electronics, the 'high' or '1' state is represented by a

A

low voltage level

B

high voltage level

C

zero voltage

D

negative voltage

49

The base of a transistor is usually of the order of

A

10^-3 m

B

10^-6 m

C

10^-9 m

D

10^-2 m