Physics Electronics Online Mcqs Test

Malik TahirLast Updated: October 13, 2025

Important Electronics Question and Answer

Total Questions:	177
Time Allowed:	60 Minutes
Total Marks:	177
How to Attempt Test:	Please choose the right Option in MCQ-type question.
Test Helpful For:	Physics Test ECAT Test MDCAT Test FPSC/PPSC/SPSC/KPPSC/BPSC/AJKPSC/NTS Physics Interview Question Answer

Physics Electronics Practice Test Online With Explanation

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1. At absolute zero, Si acts as

None of these

Insulator

Metal

Non-metal

2. The impurity atoms with which a pure silicon should be doped to make a p-type semiconductor is

Antimony

Phosphorus

Arsenic

Aluminum

3. In comma emitter amplifier (l₀/lE) = 0.98, then current gain is

4.9

9.8

4. Conversion of low input a.c. into high output a.c. is called:

Rectification

Amplification

All of these

Magnification

5. What input values will cause an AND logic gate to produce a HIGH output?

All inputs are LOW

At least one input is HIGH

At least one input is LOW

All inputs are HIGH

6. In the middle of the depletion layer of a reverse-biased p-n junction, the

Electric field is zero

Potential is zero

Potential is maximum

Electric field is maximum

7. Semi-conductors with donor atoms and free electrons belong to the type

mix

any of above

8. To obtain a p-type germanium semiconductor, it must be doped with

Phosphorus

Antimony

Indium

Arsenic

9. Which logic gate is represented by following diagram?

EOR

NOR

AND

10. The ratio β shows the

Current gain

Input resistance

Voltage gain

None of these

11. A device for converting an alternating current into a pulsating from or direct current is known as

Oscillator

Rectifier

None of these

Detector

12. The transistor provide good power amplification when they are used in

Common collector configuration

Common emitter configuration

None of these

Common base configuration

13. The measure of deformation of a solid when stress is applied to it is called

Force

Stress

None of these

Strain

14. On increasing the reverse bias to a large value in a p-n junction diode current

Decreases slowly

Remain fixed

Suddenly increases

Increases slowly

15. A p-n junction has a thickness of the order of:

1 cm

1 mm

10¯⁶ cm

10¯¹² cm

16. In forward bias, the width of potential barrier in a p-n junction diode

Remains constant

Decreases

First A and B

Increases

17. In a semiconductor, the mobility of holes is

Equal to electrons

Less than electrons

Greater than electrons

None

18. Using OP-Amp as an inverting amplifier, the non-inverting terminal has potential

Zero

Low

None of these

High

19. In Germanium crystal, impurity donor elements have valiancy

20. A diode as a rectifier converts:

Low voltage to high voltage

High voltage to low voltage

A.C. into D.C.

D.C. into A.C.

21. With negative feedback, the returning signal:

Is proportional to differential voltage gain

Is proportional to output current

Aids the input signal

Opposes the input signal

22. The positive sign of gain indicates that

None of these

May be in phase or not

Input and out signals are in phase

Input and out signals are not in phase

23. In n-p-n transistor, p works as

Base

Collector

Emitter

Any of above

24. Diode can work as

Modulator

Rectifier

Oscillator

Multivibrator

25. The operation of a transistor requires

That the collector be heated

None of these

That the emitter be heated

That the base be heated

26. Which of the following when added as an impurity into the silicon produces n-type semi-conductor?

27. Barrier potential of a p-n junction diode does not depend on:

Temperature

Diode design

Doping density

Forward bias

28. Copper and germanium are cooled to 70 K from room temperature, then

Resistance of copper increases while that of germanium decreases

Resistance of copper decreases while that of germanium increases

Resistance of both decreases

Resistance of both increases

29. When n-p-n transistor is used as an amplifier,

Holes move from emitter to base

Electrons move from base to collector

Holes move from emitter to base

Holes move from base to emitter

30. A junction between p-type material and n-type material is called as

Amplifier

Transistor

Rectifier

Diode

31. Which of the following is not characteristic of an op—amp

It offers a very low output resistance

It offers a very high inputs resistance to the input current

It offers a very low open loop gain all of above

None of these

32. The ratio of tensile stress to tensile strain is called

None of these

Modulus of electricity

Young’s modulus

Bulk’s modulus

33. When a p-n junction diode is reverse biased, the flow of current across the junction is mainly due to

Depends upon the nature of material

Both drift and diffusion of charges

Diffusion of charges

Drift of charges

34. Which is normal used of transistor?

Switching device

Diode

Rectifier

P-type material

35. The critical temperature for mercury is

4.2 K

3.72 K

1.18 K

7.2 K

36. In a junction diode, the holes are due to

Extra electrons

Protons

Missing of electrons

Neutrons

37. In junction diode, the holes are because of:

Protons

Extra electrons

Neutrons

Missing electrons

38. Application of photodiode is/are

Automatic switching

Logic gates

None of these

Detection of visible and invisible radiations

39. At absolute zero, Si acts as

Insulator

Non-metal

None of these

Metal

40. In common emitter amplifier (l₀/lE) = 0.98, then current gain is

9.8

4.9

41. N-type crystal is

Neutral

Negative charged

None of these

Positively charged

42. When aluminum is added as an impurity to silicon, then resulting material is

p-type semiconductor

n-type semiconductor

p-type conductor

n-type conductor

43. In forward bias the width of potential barrier

Remains same

Decreases

Increases

No effect

44. In insulators

Conduction band is filled with electrons and valence band is empty

Conduction band is empty and valence band is filled with electrons

Valence band is partially filled with electrons

Conduction band is partially filled with electrons

45. A diode as a rectifier converts:

High voltage to low voltage

Low voltage to high voltage

D.C. into A.C.

A.C. into D.C.

46. To use a transistor as an amplifier

No bias voltages are required

Both junctions are reverse biased

The emitter base junction is forward biased and the base collector junction is reverse biased

Both junctions are forward biased

47. When a strength changes the length of a body, it is called

Tensile stress

Shear stress

None of these

Compress ional stress

48. Suitable impurities are added to a semiconductor depending on its use. This is due to

Enable it to Telerate higher voltage

Increase its electrical resistivity

Increase its electrical conductivity

Increase its life

49. Zener breakdown in a semiconductor diode occurs when

Reverse bias exceeds certain value

Potential barrier is reduced to zero

Forward bias exceeds certain value

Forward current exceeds certain value

50. In half wave rectification

None of these

Current flows in pulses

Current flows in one directions

Only half cycle is used

51. In insulators

Conduction band is partially filled with electrons

Conduction band is empty and valence band is filled with electrons

Valence band is partially filled with electrons

Conduction band is filled with electrons and valence bad is empty

52. The especially designed semiconductor diodes used as indicator lamps in electronic circuits are

The photo diodes

The switch

Solar cells

The light emitting diode

53. If a signal passing through a gate is inhibited by sending a low into one of the inputs, and the output is HIGH, the gate is a(n):

NOR

NAND

AND

54. Which one is forward bias?

55. Depletion layer consists of

Protons

Mobile ions

Immobile ions

Electrons

56. In a P-type semiconductor

Major current carriers are electrons

The no. of mobile holes exceeds the no. of mobile acceptors

Major current carriers are mobile negative ions

Major current carriers are mobile holes

57. In a p-type semiconductor germanium is doped with:

All of above

Gallium

Aluminum

Boron

58. In the middle of the depletion layer of a reverse-biased p-n junction, the

Potential is maximum

Electric field is maximum

Potential is zero

Electric field is zero

59. The units of modulus of elasticity are same as that of

Force

None of these

Strain

Stress

60. Semi-conductor germanium and silicon are

Trivalent

Divalent

Tetravalent

Pentavalent

61. The forward resistance of the diode is

Ohms

Many ohms

Few ohms

None of these

62. Which one is reverse-biased?

63. LDR means:

Light dependent resistance

Low degree resistor

Low degree radiations

None of these

64. A n-p-n transistor conducts when

Collector is positive and emitter is at negative potential as the base

Both collector and emitter are negative with respect to the base

Both collector and emitter are positive with respect to the base

Collector is positive and emitter is negative with respect to the base

65. Arsenic, antimony or phosphorus are impurities of

p-type

n-type

may be p-type or n-type

None of these

66. In a P-type semiconductor

Major current carriers are mobile holes

The no. of mobile holes exceeds the no. of mobile acceptors

Major current carriers are electrons

Major current carriers are mobile negative ions

67. In a good conductor, the energy gap between the conduction band and the valence band is

Narrow

Wide

Infinity

Zero

68. The electrical circuit used to have smooth DC output from a rectifier circuit is called

Logic gates

Oscillator

Amplifier

Filter

69. When no light is incident on photodiode, the reverse current is

Very high

Zero

Almost negligible

Very low

70. In junction diode, the holes are because of:

Extra electrons

Protons

Missing electrons

Neutrons

71. Reverse bias applied on a junction diode

Lowers the potential barrier

Raises the potential barrier

Increase the minority carrier current

Increases the majority carrier current

72. The semiconductor diode can be used as a rectifier because _

Its conductivity increases with rise of temperature

It has low resistance to the current flow when forward biased

It has high resistance to the current flow when reverse biased

It has low resistance to the current flow when forward biased & high resistance when reverse biased

73. The basic logic gate whose output is the complement of the input is the:

AND gate

INVERTER gate

OR gate

Comparator

74. Two inputs of NAND gates are shorted. This gate is equivalent to

NOT gate

XOR gate

AND gate

OR gate

75. Due to the break down the p-n junction suffers

Require more current

Damaged

Works efficiently

None of these

76. When a pentavalent material like As, is added to tetravalent material l.e. Ge, we get a

Super conductor

Semiconductor

P-type material

N-type material

77. The energy band gap is maximum in

Superconductors

Metals

Semiconductors

Insulators

78. A photodiode can turn its current ON and OFF in

None of these

Nanosecond

Millisecond

Microsecond

79. The logic gate that will have HIGH or “1” at its output when any one of its input if HIGH is a(n):

NOR gate

OR gate

AND gate

NOT gate

80. The thickness of the base is equal to

Mean of thickness of emitter and collector

Thickness of collector

Thickness of emitter

Very small as compared to the thickness of emitter and collector

81. In a PN junction

High potential at P side and low potential at N side

P and N both are at same potential

Undetermined

High potential at N side and low potential at P side

82. When n-p-n transistor is used as an amplifier

Electrons move from base to collector

Holes move from emitter be base

Holes move from base to emitter

Holes move from emitter to base

83. In semiconductors at a room temperature

The valence band is completely filled and the conduction band is partially filled

The conduction band is completely empty

The valence band is partially empty and the conduction band is partially filled

The valence band is completely filled

84. A non-inverting closed-loop op-amp circuit generally has a gain factor:

Equal to one

Greater than one

Of zero

Less than one

85. A signal applied at the non-inverting input, of an O.P that appears after amplification at the output terminal, with

180° Phase shift

No Phase shift

120° Phase shift

90° Phase shift

86. In a n-p-n transistor:

Holes move from emitter to base

Negative charge moves from emitter to base

Holes move from base to collector

Negative charge moves from collector to base

87. p-n junction when reversed biased acts as a

On switch

Capacitor

Inductor

Off switch

88. When a semiconductor is continuously heated, then value of its resistance

Increases

Decreases

Decreases and then increases

Remains unchanged

89. When an alternating accelerating field is applied to a charge it produces

Gamma Rays

x-rays

Transverse Waves

Electromagnetic Waves

90. NAND gate is

A universal gate

A basic gate

A basic universal gate

Not a universal gate

91. When n-type of semiconductor is heated,

Number of electrons and holes increases equally

Number of electrons increases while that of holes decreases

Number of holes increases while that of holes decreases

Number of electrons and holes remains same

92. The electromagnetic waves emitted by the LC circuit of areal to a transmitting station are of

Unit amplitude

Constant amplitude

Variable amplitude

Zero amplitude

93. The electrons in the outermost shell of an atom are called

Free electrons

None of these

Valence electrons

Tightly bound electrons

94. The ratio of applied stress to volumetric strain is called

Shear modulus

Young’s modulus

Bulk modulus

None of these

95. n-type semiconductor if formed

When a Ge crystal is doped with an impurity containing 3 valence electrons

From pure Si crystal

When a Ge crystal is doped with an impurity containing 5 valence electrons

From pure Ge crystal

96. The part of a transistor, which is heavily doped to produce a large number of majority carriers, is

Collector

Base

Emitter

None of these

97. In a p-type semiconductor germanium is doped with:

All of these

Aluminum

Gallium

Boron

98. The gain A of the amplifier is of the order of

Thousands

None of these

Man hundred

Hundreds

99. When the conductivity of a semiconductor is only due to breaking of covalent bonds, the semiconductor is called

Intrinsic

n-type

p-type

Extrinsic

100. When we apply reverse bias to a junction diode, it

Increase the majority carrier current

Raises the potential barrier

Lowers the potential barrier

Increase the minority carrier current

101. In a n-p-n transistor:

Holes move from base to collector

Negative charge moves from collector to base

Holes move from emitter to base

Negative charge moves from emitter to base

102. The part of a transistor which is most heavily doped to produce large number of majority carriers is

Can be any of the above three

Emitter

Collector

Base

103. If on increasing temperature the resistance decreases, then it is

None of these

Insulator

Superconductor

Semiconductor

104. The materials in which valence band and conduction band overlap are called

Semiconductors

Conductors

Superconductors

Insulators

105. The width of a depletion layer in a p-n junction is

Decreased by reverse biasing

Is independent of voltage

Increased by forward biasing

Increased by reverse biasing

106. When arsenic is added as an impurity to silicon, the resulting material is

N-type semiconductor

None of these

N-type conductor

P-type semiconductor

107. In p-type semiconductor

The number of mobile holes exceeds the number of acceptors

Major carrier is mobile negative ions

Major carrier is mobile holes

Major current carrier is electrons

108. A pieced of copper and another of germanium are cooled from room temperature to 77 K, the resistance of

Copper decreases and germanium increases

Each of them decreases

Copper increases and germanium decreases

Each of them increases

109. In semiconductors at a room temperature

The valence band is completely filled and the conduction band is partially filled

The valence band is partially empty and the conduction band is partially filled

The conduction band is completely empty

The valence band is completely filled

110. In p-type semi-conductor, the majority charge carriers are

Protons

Neutrons

Holes

Electrons

111. When the output of OR gate is 1

Only if both inputs are 1

If either input is zero

If either or both inputs are 1

If both inputs are zero

112. The potential difference across the depletion region of silicon is

0.67 V

0.9 V

0.5 V

0.7 V

113. Transistors with various combinations are widely used as switches in:

Transformers

Electric generations

Computers

Electric motors

114. At room temperature, a p-type semi-conductor has

Large number of holes and few electrons

Large number of free electrons and few holes

Equal number of free electrons and holes

Large number of holes and electrons

115. Output voltage in full wave rectification is not smooth. In order to have smooth output voltage

Resistor is used

Solvent is used

None of these

Capacitor is used

116. The whole structure obtained by the repetition of unit cell is known as

Crystal lattice

All of these

Unit cell

Ore

117. A piece of copper and another of germanium are cooled from room temperature to 77 K, the resistance of

Each of them increases

Each of them decreases

Copper decreases and germanium increases

Copper increases and germanium decreases

118. Symbol represents

NOT gate

NAND gate

NOR gate

XNOR gate

119. A substance which have empty conduction band is called

None of these

Semiconductor

Conductor

Insulator

120. A device which converts an alternating current to direct current is called

Oscillator

Amplifier

P-type material

Rectifier

121. The energy gap between conduction band and valence band is order 0.07 eV. It is a

Alloy

Insulator

Semiconductor

Conductor

122. Photovoltaic cell produces electrical energy from

Light energy

None of these

Heat energy

Chemical energy

123. The least doped region in a transistor is

Emitter

Base

Collector

124. The number of junctions in the PNP transistor are

125. When Ge crystal is doped with phosphorus atom, then it becomes

n-type

p-type

Insulator

Superconductor

126. The width of a depletion layer in a p-n junction is

Increased by forward biasing

Decreased by reverse biasing

Increased by reverse biasing

Is independent of voltage

127. Due to high loop gain of the amplifier, the inverting and non-inverting inputs are

Both are at the same potential

Both are at the high potential

Inverting terminal is at high potential

Non-inverting terminal is at high potential

128. A transistor consists of

One PN-junction

Two PN-junctions

Three PN-junctions

Four PN-junctions

129. In reverse biasing of p-n junction, the resistance offered by the diode is of the order of

Kilo ohms

Ohms

Mega ohms

Several mega ohms

130. When boron is added as an impurity to silicon, the resulting material is:

n-type conductor

p-type conductor

p-type semiconductor

n-type semiconductor

131. Transistor can be used as

Filter

Half wave rectifier

Full wave rectifier

Amplifier

132. The least doped region in a transistor is

Emitter

Either emitter or collector

Collector

Base

133. A NAND gate has:

HIGH inputs and a HIGH output

None of these

LOW inputs and a LOW output

LOW inputs and a HIGH output

134. Depletion region of a junction is formed

During the manufacturing process

Under reverse bias

When temperature varies

Under forward bias

135. When a semiconductor is continuously heated, then value of its resistance

Increases

Remains unchanged

Decreases

Decreases and then increases

136. In the transistor schematic symbol, the arrow

Is locate on the collector

Is located on the base

Is located on the emitter

Point from north to south

137. If positive end of battery is connected to p-side and negative end of battery is connected to n-side of diode then

None of these

Diode is forward biased

Diode is neutralized

Diode is reverse biased

138. The ratio β represents

139. The electrical circuit used to bet smooth DC output from a rectifier circuit is called

Filter

Logic gates

Oscillator

Amplifier

140. p-type crystal of a p-n junction diode is connected to a positive terminal of battery and n-type crystal connected to negative terminal of battery

Potential barrier in depletion layer increases

Diode is forward based

Potential barrier in depletion layer remains unchanged

Diode is reverse biased

141. Polythene, potystrene and nylon are examples of

Amorphous solids

Glassy solids

Polymeric solids

Crystalline solids

142. n-type germanium is obtained on doping intrinsic germanium with

Gold

Phosphorus

Boron

Aluminum

143. The simplest type of rectification known as half wave rectification is obtained by

Using a Coolidge tube

Using a transistor

Suppressing half wave of A.C supply by using diode

Suppressing the harmonics in A.C voltage

144. Exclusive-OR (XOR) logic gates can be constructed from what other logic gates?

Or gates and NOT gates

AND gates, OR gates, and NOT gates

AND gates and NOT gates

OR gates only

145. In n-type substances, the minority carriers are

None of these

Electrons

Neutrons

Holes

146. In p – n junction, after diffusion, a charge less region is formed around the junction is called

None of these

Diffusion region

Charged region

Depletion region

147. Non-inverting amplifier circuits have

A very low input impedance

A low output impedance

None of these

A very high input impedance

148. Identify the correct statement about minority carriers

Free electrons in n-type and p-type

Holes in n-type and p-type

Free electrons in n-type and holes in p-type

Holes in n-type and free electrons in p-type

149. The switch is open when the resistance between C and E becomes

Infinity

Almost zero

Zero

None of these

150. The p-n junction diode works as insulator, if connected

To A.C.

In reverse bias

None of these

In forward bias

151. The impurity atoms with which a pure silicon should be doped to make a p-type semiconductor is

Arsenic

Phosphorus

Aluminum

Antimony

152. Young’s modulus for copper is

91 x 10 Nm¯²

None of these

70 x 10 Nm¯²

110 Nm¯²

153. Light emitting diode work when it is

Forward biases

None of these

Reverse biased

Both

154. A single transistor can be used to build which of the following digital logic gates?

AND gates

OR gates

NAND gates

NOT gates

155. At room temperature, a p-type semi-conductor has

Large number of holes and few electrons

Equal number of free electrons and holes

Large number of holes and electrons

Large number of free electrons and few holes

156. Photodiode is used for

Emission of light

Light display

Detection of light

None of these

157. When the conductivity of a semiconductor is only due, to breaking of covalent bonds, the semiconductor is called

Intrinsic

p-type

Extrinsic

n-type

158. Electrons present in p-type material due to thermal pair generation are

Majority carriers

Blockers

Minority carriers

Dual carriers

159. When NPN transistor is used as an amplifier

Holes move from base to emitter

Electrons move from collector to base

Electrons move from emitter to base

Electrons move from base to emitter

160. Reverse bias applied on a junction diode

Increase the minority carrier current

Lowers the potential barrier

Increases the majority carrier current

Raises the potential barrier

161. Suitable impurities are added to a semiconductor depending on its use. This is due to:

Enable it to Telerate higher voltage

Increases its electrical conductivity

Increase its electrical resistivity

Increase its life

162. The output will be a LOW for any case when one or more inputs are zero in a(n):

AND gate

OR gate

NOT gate

NAND gate

163. In the p-type semi-conductor the majority and minority charge carriers are respectively

Electrons and protons

Holes and electrons

Electrons and holes

Protons and electrons

164. When aluminum is added as an impurity to silicon, then resulting material is

p-type semiconductor

p-type conductor

n-type conductor

n-type semiconductor

165. In Germanium crystal, impurity donor elements have valiancy

166. An OP-AMPs can amplify

A.C.

None of these

D.C.

Both A.C. & D.C.

167. Acceptor and donor impurities donate

p-carriers and n-carriers respectively

n-carriers only

n-carriers and p-carriers respectively

p-carriers only

168. The energy band gap is maximum in

Insulators

Semiconductors

Metals

Superconductors

169. The device or circuit used for conversion of A.C. into D.C. is called

Converter

Filtering circuit

An amplifier

A rectifier

170. In between two consecutive permissible energy bands, there is a range of energy states which cannot be occupied by electrons. These are called

Hidden energy states

Forbidden energy states

Band levels

None of these

171. The working of transistor as amplifier is similar to

Step up transformer

Step down transformer

Three diodes in common

Triode vacuum tube

172. If p-type material of the PN-junction is connected with positive terminal of the battery and n-type material with negative terminal of the battery, it is said to be

None of these

Zero biased

Forward biased

Reversed biased

173. The part of a transistor which is heavily doped to produce large number of majority carriers is

Base

Emitter

Collector

Any of the above depending on nature of transistor

174. An OP-AMP comparator is a circuit that compares the signal voltage on one of its inputs with a _

Output

Non-inverting voltage at output

Reference voltage on the other

Virtual input

175. In p-n-p transistor the collector current is

Slightly less than emitter current

Equal to emitter current

Greater than emitter current

Any of above

176. Radio waves of constant amplitude can be generated with

Filter

FET

Rectifier

Oscillator

177. The part of a transistor which is most heavily doped to produce large number of majority carriers is

Emitter

Base

Collector

Can be any of the above three

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