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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.
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Physics Electronics Practice Test Online With Explanation

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1. The forward resistance of the diode is

Few ohms

Ohms

None of these

Many ohms

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

Require more current

Works efficiently

Damaged

None of these

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

Less than one

Of zero

Equal to one

Greater than one

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

Amplifier

Oscillator

P-type material

Rectifier

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

None of these

Nanosecond

Microsecond

Millisecond

6. Identify the correct statement about minority carriers

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

Holes in n-type and p-type

Free electrons in n-type and p-type

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

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

Potential is maximum

Potential is zero

Electric field is zero

Electric field is maximum

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

Off switch

Inductor

On switch

Capacitor

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

Is independent of voltage

Decreased by reverse biasing

Increased by forward biasing

Increased by reverse biasing

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

n-type semiconductor

n-type conductor

p-type conductor

p-type semiconductor

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

Emitter

Any of the above depending on nature of transistor

Base

Collector

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

Protons

Missing electrons

Extra electrons

Neutrons

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

None of these

Infinity

Zero

Almost zero

14. Young’s modulus for copper is

91 x 10 Nm¯²

None of these

70 x 10 Nm¯²

110 Nm¯²

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

NOT gate

OR gate

AND gate

NOR gate

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

Emitter

Any of above

Collector

Base

17. 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

Collector

Base

Emitter

18. Semi-conductor germanium and silicon are

Trivalent

Tetravalent

Pentavalent

Divalent

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

Tensile stress

None of these

Compress ional stress

Shear stress

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

n-type semiconductor

p-type semiconductor

n-type conductor

p-type conductor

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

Charged region

Depletion region

None of these

Diffusion region

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

Missing of electrons

Extra electrons

Protons

Neutrons

23. Photodiode is used for

None of these

Detection of light

Emission of light

Light display

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

Gamma Rays

x-rays

Transverse Waves

Electromagnetic Waves

25. A n-p-n transistor conducts when

Both collector and emitter are negative with respect to the base

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

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

Both collector and emitter are positive with respect to the base

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

Free electrons

Valence electrons

None of these

Tightly bound electrons

27. An OP-AMPs can amplify

A.C.

Both A.C. & D.C.

None of these

D.C.

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

First A and B

Remains constant

Decreases

Increases

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

Comparator

AND gate

INVERTER gate

OR gate

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

High

Low

Zero

None of these

31. Depletion region of a junction is formed

During the manufacturing process

When temperature varies

Under forward bias

Under reverse bias

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

Copper increases and germanium decreases

Copper decreases and germanium increases

Each of them increases

Each of them decreases

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

Increased by forward biasing

Increased by reverse biasing

Decreased by reverse biasing

Is independent of voltage

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

AND gates and NOT gates

AND gates, OR gates, and NOT gates

Or gates and NOT gates

OR gates only

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

Semiconductors

Superconductors

Insulators

Conductors

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

Filtering circuit

Converter

A rectifier

An amplifier

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

Decreases and then increases

Decreases

Remains unchanged

Increases

38. LDR means:

Low degree resistor

Light dependent resistance

None of these

Low degree radiations

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

Greater than emitter current

Equal to emitter current

Slightly less than emitter current

Any of above

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

Intrinsic

n-type

Extrinsic

p-type

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

Transistor

Amplifier

Rectifier

Diode

42. 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

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

mix

any of above

44. Depletion layer consists of

Immobile ions

Mobile ions

Electrons

Protons

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

It offers a very high inputs resistance to the input current

It offers a very low output resistance

None of these

It offers a very low open loop gain all of above

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

120° Phase shift

180° Phase shift

No Phase shift

90° Phase shift

47. NAND gate is

Not a universal gate

A basic universal gate

A universal gate

A basic gate

48. 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

Forward biased

Reversed biased

Zero biased

49. Which one is reverse-biased?

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

Variable amplitude

Constant amplitude

Zero amplitude

Unit amplitude

51. N-type crystal is

None of these

Neutral

Positively charged

Negative charged

52. The energy band gap is maximum in

Insulators

Semiconductors

Superconductors

Metals

53. To use a transistor as an amplifier

Both junctions are forward biased

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

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

Holes and electrons

Protons and electrons

Electrons and protons

Electrons and holes

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

Increase its electrical resistivity

Increases its electrical conductivity

Enable it to Telerate higher voltage

Increase its life

56. Transistor can be used as

Filter

Amplifier

Full wave rectifier

Half wave rectifier

57. The least doped region in a transistor is

Emitter

Base

Collector

Either emitter or collector

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

Non-inverting voltage at output

Virtual input

Reference voltage on the other

Output

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

All of these

Crystal lattice

Ore

Unit cell

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

Thousands

None of these

Hundreds

Man hundred

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

Semiconductor

Superconductor

None of these

Insulator

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

AND gate

NOT gate

XOR gate

OR gate

63. In half wave rectification

Current flows in pulses

None of these

Current flows in one directions

Only half cycle is used

64. The ratio β represents

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

Electric motors

Electric generations

Transformers

Computers

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

p-type semiconductor

p-type conductor

n-type semiconductor

n-type conductor

67. In a semiconductor, the mobility of holes is

Less than electrons

None

Equal to electrons

Greater than electrons

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

AND gates

OR gates

NOT gates

NAND gates

69. In a n-p-n transistor:

Holes move from base to collector

Holes move from emitter to base

Negative charge moves from collector to base

Negative charge moves from emitter to base

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

Shear modulus

None of these

Bulk modulus

Young’s modulus

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

Dual carriers

Blockers

Minority carriers

Majority carriers

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

Boron

Gold

Phosphorus

Aluminum

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

Large number of free electrons and few holes

Large number of holes and few electrons

Large number of holes and electrons

Equal number of free electrons and holes

74. Radio waves of constant amplitude can be generated with

Oscillator

Filter

FET

Rectifier

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

Mega ohms

Kilo ohms

Several mega ohms

Ohms

76. Zener breakdown in a semiconductor diode occurs when

Potential barrier is reduced to zero

Reverse bias exceeds certain value

Forward bias exceeds certain value

Forward current exceeds certain value

77. When the output of OR gate is 1

If both inputs are zero

Only if both inputs are 1

If either or both inputs are 1

If either input is zero

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

9.8

4.9

79. Diode can work as

Oscillator

Multivibrator

Modulator

Rectifier

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

Indium

Antimony

Arsenic

Phosphorus

81. In a P-type semiconductor

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

Major current carriers are mobile negative ions

Major current carriers are electrons

Major current carriers are mobile holes

82. Which one is forward bias?

83. Symbol represents

NAND gate

NOT gate

XNOR gate

NOR gate

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

Zero

Narrow

Wide

Infinity

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

Boron

Gallium

Aluminum

All of these

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

All inputs are HIGH

At least one input is LOW

At least one input is HIGH

All inputs are LOW

87. The working of transistor as amplifier is similar to

Triode vacuum tube

Step down transformer

Three diodes in common

Step up transformer

88. n-type semiconductor if formed

From pure Ge crystal

From pure Si crystal

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

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

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

Resistance of both decreases

Resistance of both increases

Resistance of copper increases while that of germanium decreases

Resistance of copper decreases while that of germanium increases

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

All of above

Boron

Gallium

Aluminum

91. 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.

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

4.9

9.8

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

Extrinsic

n-type

Intrinsic

p-type

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

Holes move from base to emitter

Electrons move from base to collector

Holes move from emitter to base

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

Logic gates

Amplifier

Oscillator

Filter

96. 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

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

Semiconductor

P-type material

Super conductor

N-type material

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

Force

None of these

Strain

Stress

99. In a PN junction

High potential at P side and low potential at N side

Undetermined

P and N both are at same potential

High potential at N side and low potential at P side

100. In Germanium crystal, impurity donor elements have valiancy

101. Which is normal used of transistor?

P-type material

Switching device

Diode

Rectifier

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

Forward bias

Diode design

Doping density

Temperature

103. 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):

AND

NOR

NAND

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

Electric field is maximum

Potential is maximum

Electric field is zero

Potential is zero

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

In forward bias

None of these

To A.C.

In reverse bias

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

0.5 V

0.9 V

0.7 V

0.67 V

107. 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

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

N-type conductor

P-type semiconductor

None of these

N-type semiconductor

109. The ratio β shows the

None of these

Current gain

Voltage gain

Input resistance

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

Suppressing half wave of A.C supply by using diode

Suppressing the harmonics in A.C voltage

Using a Coolidge tube

Using a transistor

111. In Germanium crystal, impurity donor elements have valiancy

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

Antimony

Phosphorus

Arsenic

Aluminum

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

Collector

None of these

Emitter

Base

114. Acceptor and donor impurities donate

p-carriers only

n-carriers and p-carriers respectively

n-carriers only

p-carriers and n-carriers respectively

115. In the transistor schematic symbol, the arrow

Point from north to south

Is located on the base

Is locate on the collector

Is located on the emitter

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

Diode is forward biased

None of these

Diode is reverse biased

Diode is neutralized

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

None of these

Common emitter configuration

Common base configuration

Common collector configuration

118. The least doped region in a transistor is

Collector

Base

Emitter

119. Reverse bias applied on a junction diode

Raises the potential barrier

Increases the majority carrier current

Lowers the potential barrier

Increase the minority carrier current

120. Non-inverting amplifier circuits have

A very high input impedance

A very low input impedance

None of these

A low output impedance

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

None of these

Solvent is used

Capacitor is used

Resistor is used

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

None of these

Stress

Force

Strain

123. In semiconductors at a room temperature

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 and the conduction band is partially filled

The valence band is completely filled

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

Neutrons

Missing electrons

Protons

Extra electrons

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

Copper increases and germanium decreases

Copper decreases and germanium increases

Each of them increases

Each of them decreases

126. At absolute zero, Si acts as

Metal

None of these

Insulator

Non-metal

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

Detector

Oscillator

Rectifier

None of these

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

Protons

Holes

Electrons

Neutrons

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

Alloy

Insulator

Conductor

Semiconductor

130. When n-type of semiconductor is heated,

Number of holes increases while that of holes decreases

Number of electrons increases while that of holes decreases

Number of electrons and holes increases equally

Number of electrons and holes remains same

131. 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

132. The thickness of the base is equal to

Thickness of emitter

Mean of thickness of emitter and collector

Very small as compared to the thickness of emitter and collector

Thickness of collector

133. A NAND gate has:

None of these

HIGH inputs and a HIGH output

LOW inputs and a LOW output

LOW inputs and a HIGH output

134. The operation of a transistor requires

That the base be heated

None of these

That the collector be heated

That the emitter be heated

135. In forward bias the width of potential barrier

Decreases

Increases

Remains same

No effect

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

Bulk’s modulus

None of these

Modulus of electricity

Young’s modulus

137. At absolute zero, Si acts as

Non-metal

Insulator

None of these

Metal

138. Application of photodiode is/are

Logic gates

Detection of visible and invisible radiations

Automatic switching

None of these

139. 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 be base

Holes move from base to emitter

140. Polythene, potystrene and nylon are examples of

Glassy solids

Amorphous solids

Polymeric solids

Crystalline solids

141. The number of junctions in the PNP transistor are

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

Increase its electrical conductivity

Enable it to Telerate higher voltage

Increase its life

Increase its electrical resistivity

143. Photovoltaic cell produces electrical energy from

None of these

Chemical energy

Light energy

Heat energy

144. 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

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

Decreases

Increases

Remains unchanged

Decreases and then increases

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

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

Large number of free electrons and few holes

Large number of holes and few electrons

Equal number of free electrons and holes

Large number of holes and electrons

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

Base

Emitter

Can be any of the above three

Collector

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

Aluminum

Phosphorus

Arsenic

Antimony

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

1 mm

10¯⁶ cm

1 cm

10¯¹² cm

151. The energy band gap is maximum in

Metals

Insulators

Superconductors

Semiconductors

152. In insulators

Conduction band is filled with electrons and valence bad is empty

Conduction band is partially filled with electrons

Valence band is partially filled with electrons

Conduction band is empty and valence band is filled with electrons

153. A substance which have empty conduction band is called

Conductor

None of these

Semiconductor

Insulator

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

Electrons

Neutrons

Holes

None of these

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

Magnification

Amplification

Rectification

All of these

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

The light emitting diode

Solar cells

The photo diodes

The switch

157. When NPN transistor is used as an amplifier

Holes move from base to emitter

Electrons move from emitter to base

Electrons move from base to emitter

Electrons move from collector to base

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

n-type

Insulator

Superconductor

p-type

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

OR gate

NOT gate

NAND gate

AND gate

160. Which logic gate is represented by following diagram?

NOR

EOR

AND

161. A diode as a rectifier converts:

D.C. into A.C.

A.C. into D.C.

Low voltage to high voltage

High voltage to low voltage

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

Oscillator

Logic gates

Filter

Amplifier

163. A transistor consists of

Two PN-junctions

Three PN-junctions

One PN-junction

Four PN-junctions

164. Arsenic, antimony or phosphorus are impurities of

may be p-type or n-type

None of these

p-type

n-type

165. 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 reverse biased

Diode is forward based

Potential barrier in depletion layer remains unchanged

166. In p-type semiconductor

Major carrier is mobile holes

The number of mobile holes exceeds the number of acceptors

Major current carrier is electrons

Major carrier is mobile negative ions

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

Zero

Very high

Almost negligible

Very low

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

Increases slowly

Remain fixed

Suddenly increases

Decreases slowly

169. Reverse bias applied on a junction diode

Raises the potential barrier

Increase the minority carrier current

Increases the majority carrier current

Lowers the potential barrier

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

Non-inverting terminal is at high potential

Both are at the high potential

Inverting terminal is at high potential

Both are at the same potential

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

Drift of charges

Depends upon the nature of material

Diffusion of charges

Both drift and diffusion of charges

172. In semiconductors at a room temperature

The conduction band is completely empty

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

The valence band is completely filled

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

173. The positive sign of gain indicates that

Input and out signals are in phase

None of these

May be in phase or not

Input and out signals are not in phase

174. With negative feedback, the returning signal:

Opposes the input signal

Is proportional to output current

Is proportional to differential voltage gain

Aids the input signal

175. The critical temperature for mercury is

7.2 K

1.18 K

3.72 K

4.2 K

176. Light emitting diode work when it is

Both

Reverse biased

Forward biases

None of these

177. In a n-p-n transistor:

Holes move from base to collector

Holes move from emitter to base

Negative charge moves from emitter to base

Negative charge moves from collector to base

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Malik TahirLast Updated: October 13, 2025

Physics Electronics Online Mcqs Test

Important Electronics Question and Answer

Physics Electronics Practice Test Online With Explanation

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