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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. 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

Potential barrier in depletion layer remains unchanged

Diode is forward based

Diode is reverse biased

2. In half wave rectification

None of these

Current flows in pulses

Current flows in one directions

Only half cycle is used

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

1 cm

1 mm

10¯¹² cm

10¯⁶ cm

4. In Germanium crystal, impurity donor elements have valiancy

5. Which one is forward bias?

6. In insulators

Valence band is partially filled with electrons

Conduction band is filled with electrons and valence bad is empty

Conduction band is empty and valence band is filled with electrons

Conduction band is partially filled with electrons

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

Emitter

Collector

Can be any of the above three

Base

8. Which is normal used of transistor?

P-type material

Rectifier

Switching device

Diode

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

Intrinsic

Extrinsic

n-type

p-type

10. In insulators

Conduction band is empty and valence band is filled with electrons

Conduction band is filled with electrons and valence band is empty

Valence band is partially filled with electrons

Conduction band is partially filled with electrons

11. At absolute zero, Si acts as

Non-metal

Metal

None of these

Insulator

12. Reverse bias applied on a junction diode

Increase the minority carrier current

Increases the majority carrier current

Lowers the potential barrier

Raises the potential barrier

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

Amplification

Rectification

All of these

Magnification

14. In a semiconductor, the mobility of holes is

Greater than electrons

Less than electrons

None

Equal to electrons

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

At least one input is HIGH

All inputs are LOW

All inputs are HIGH

At least one input is LOW

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

Amplifier

Oscillator

Filter

Logic gates

17. LDR means:

Low degree radiations

None of these

Low degree resistor

Light dependent resistance

18. 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.

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

None of these

Collector

Base

Emitter

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

None of these

Infinity

Zero

Almost zero

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

Superconductor

Semiconductor

None of these

Insulator

22. Photovoltaic cell produces electrical energy from

None of these

Chemical energy

Heat energy

Light energy

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

It has high resistance to the current flow when reverse biased

Its conductivity increases with rise of temperature

It has low resistance to the current flow when forward biased

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

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

Remain fixed

Decreases slowly

Increases slowly

Suddenly increases

25. NAND gate is

A universal gate

A basic gate

A basic universal gate

Not a universal gate

26. 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 increases and germanium decreases

Copper decreases and germanium increases

27. 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 only

Or gates and NOT gates

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

Rectifier

Diode

Transistor

Amplifier

29. A diode as a rectifier converts:

Low voltage to high voltage

A.C. into D.C.

D.C. into A.C.

High voltage to low voltage

30. At absolute zero, Si acts as

Non-metal

None of these

Insulator

Metal

31. Young’s modulus for copper is

110 Nm¯²

70 x 10 Nm¯²

None of these

91 x 10 Nm¯²

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

Zero

Low

High

None of these

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

Transformers

Electric motors

Electric generations

Computers

34. The critical temperature for mercury is

3.72 K

1.18 K

4.2 K

7.2 K

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

Boron

Gallium

Aluminum

All of above

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

Aluminum

Boron

Gallium

All of these

37. The working of transistor as amplifier is similar to

Step down transformer

Three diodes in common

Step up transformer

Triode vacuum tube

38. Reverse bias applied on a junction diode

Increases the majority carrier current

Increase the minority carrier current

Raises the potential barrier

Lowers the potential barrier

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

Works efficiently

Damaged

Require more current

None of these

40. The forward resistance of the diode is

Many ohms

Few ohms

Ohms

None of these

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

Equal number of free electrons and holes

Large number of holes and electrons

Large number of holes and few electrons

Large number of free electrons and few holes

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

Tightly bound electrons

Free electrons

None of these

Valence electrons

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

Large number of free electrons and few holes

Large number of holes and electrons

Equal number of free electrons and holes

Large number of holes and few electrons

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

Insulator

Superconductor

n-type

p-type

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

Of zero

Equal to one

Less than one

Greater than one

46. In a P-type semiconductor

Major current carriers are electrons

Major current carriers are mobile holes

Major current carriers are mobile negative ions

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

47. In the transistor schematic symbol, the arrow

Is located on the emitter

Is locate on the collector

Point from north to south

Is located on the base

48. When n-type of semiconductor is heated,

Number of holes increases while that of holes decreases

Number of electrons and holes remains same

Number of electrons and holes increases equally

Number of electrons increases while that of holes decreases

49. 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

Diode is reverse biased

Diode is neutralized

None of these

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

Extrinsic

Intrinsic

n-type

p-type

51. Arsenic, antimony or phosphorus are impurities of

None of these

n-type

may be p-type or n-type

p-type

52. Photodiode is used for

Emission of light

Light display

Detection of light

None of these

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

NOT gates

OR gates

NAND gates

AND gates

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

Electrons and holes

Electrons and protons

Protons and electrons

Holes and electrons

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

Collector

Emitter

Base

Any of the above depending on nature of transistor

56. A substance which have empty conduction band is called

Insulator

Semiconductor

Conductor

None of these

57. The least doped region in a transistor is

Emitter

Either emitter or collector

Collector

Base

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

Electric field is maximum

Potential is zero

Potential is maximum

Electric field is zero

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

None of these

Thousands

Man hundred

Hundreds

60. Identify the correct statement about minority carriers

Free electrons 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

Holes in n-type and p-type

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

Potential is zero

Electric field is maximum

Electric field is zero

Potential is maximum

62. 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

63. Diode can work as

Multivibrator

Rectifier

Modulator

Oscillator

64. The ratio β represents

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

Is independent of voltage

Increased by forward biasing

Decreased by reverse biasing

Increased by reverse biasing

66. Polythene, potystrene and nylon are examples of

Polymeric solids

Glassy solids

Crystalline solids

Amorphous solids

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

None of these

Holes

Electrons

Neutrons

68. In a PN junction

Undetermined

High potential at P side and low potential at N side

P and N both are at same potential

High potential at N side and low potential at P side

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

Collector

Base

Any of above

Emitter

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

Tensile stress

Shear stress

Compress ional stress

None of these

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

Holes

Electrons

Neutrons

Protons

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

P-type material

Semiconductor

Super conductor

N-type material

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

Greater than emitter current

Slightly less than emitter current

Equal to emitter current

Any of above

74. Depletion region of a junction is formed

Under forward bias

During the manufacturing process

Under reverse bias

When temperature varies

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

Is independent of voltage

Decreased by reverse biasing

Increased by reverse biasing

Increased by forward biasing

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

n-type conductor

p-type semiconductor

p-type conductor

n-type semiconductor

77. In a n-p-n transistor:

Negative charge moves from emitter to base

Holes move from base to collector

Holes move from emitter to base

Negative charge moves from collector to base

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

Increases

Decreases

Remains constant

First A and B

79. Radio waves of constant amplitude can be generated with

FET

Oscillator

Rectifier

Filter

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

It offers a very low open loop gain all of above

It offers a very high inputs resistance to the input current

None of these

It offers a very low output resistance

81. 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

82. 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 mobile negative ions

Major current carriers are electrons

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

Resistance of copper decreases while that of germanium increases

Resistance of copper increases while that of germanium decreases

Resistance of both decreases

Resistance of both increases

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

Non-inverting voltage at output

Output

Reference voltage on the other

Virtual input

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

Force

Strain

Stress

None of these

86. The operation of a transistor requires

That the collector be heated

That the emitter be heated

None of these

That the base be heated

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

Phosphorus

Arsenic

Aluminum

Antimony

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

None of these

Young’s modulus

Modulus of electricity

Bulk’s modulus

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

Converter

An amplifier

Filtering circuit

A rectifier

90. Semi-conductor germanium and silicon are

Pentavalent

Tetravalent

Trivalent

Divalent

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

Very high

Almost negligible

Very low

Zero

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

Comparator

OR gate

INVERTER gate

AND gate

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

Both drift and diffusion of charges

Diffusion of charges

Depends upon the nature of material

Drift of charges

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

Protons

Extra electrons

Missing of electrons

Neutrons

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

Protons

Missing electrons

Extra electrons

Neutrons

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

Insulator

Conductor

Semiconductor

Alloy

97. In forward bias the width of potential barrier

Increases

Decreases

No effect

Remains same

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

Oscillator

Amplifier

Logic gates

Filter

99. 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

Zero biased

Reversed biased

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

Ohms

Kilo ohms

Mega ohms

Several mega ohms

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

None of these

Capacitor is used

Solvent is used

Resistor is used

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

NOT gate

OR gate

NAND gate

AND gate

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

None of these

Depletion region

Charged region

Diffusion region

104. Depletion layer consists of

Protons

Mobile ions

Electrons

Immobile ions

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

Unit cell

Ore

Crystal lattice

All of these

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

Neutrons

Extra electrons

Missing electrons

Protons

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

Aluminum

Phosphorus

Gold

Boron

108. A n-p-n transistor conducts when

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 negative with respect to the base

Both collector and emitter are positive with respect to the base

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

0.67 V

0.7 V

0.5 V

0.9 V

110. Which one is reverse-biased?

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

Antimony

Arsenic

Aluminum

Phosphorus

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

Rectifier

Oscillator

P-type material

Amplifier

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

Increase its electrical resistivity

Increase its life

Enable it to Telerate higher voltage

Increase its electrical conductivity

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

Strain

Force

None of these

Stress

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

Remains unchanged

Increases

Decreases and then increases

Decreases

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

Copper increases and germanium decreases

Each of them increases

Copper decreases and germanium increases

Each of them decreases

117. The number of junctions in the PNP transistor are

118. 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

119. An OP-AMPs can amplify

D.C.

Both A.C. & D.C.

None of these

A.C.

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

p-type semiconductor

p-type conductor

n-type semiconductor

n-type conductor

121. 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

122. The positive sign of gain indicates that

None of these

Input and out signals are in phase

Input and out signals are not in phase

May be in phase or not

123. Application of photodiode is/are

Automatic switching

Logic gates

Detection of visible and invisible radiations

None of these

124. In p-type semiconductor

Major carrier is mobile holes

Major current carrier is electrons

The number of mobile holes exceeds the number of acceptors

Major carrier is mobile negative ions

125. Acceptor and donor impurities donate

p-carriers and n-carriers respectively

n-carriers only

n-carriers and p-carriers respectively

p-carriers only

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

Arsenic

Phosphorus

Indium

Antimony

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

P-type semiconductor

N-type semiconductor

None of these

N-type conductor

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

Majority carriers

Blockers

Dual carriers

Minority carriers

129. Light emitting diode work when it is

None of these

Reverse biased

Forward biases

Both

130. 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

131. N-type crystal is

Neutral

Positively charged

Negative charged

None of these

132. In Germanium crystal, impurity donor elements have valiancy

133. The ratio β shows the

Input resistance

None of these

Voltage gain

Current gain

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

180° Phase shift

90° Phase shift

120° Phase shift

No Phase shift

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

None of these

Millisecond

Microsecond

Nanosecond

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

Band levels

None of these

Forbidden energy states

Hidden energy states

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

Common collector configuration

Common base configuration

Common emitter configuration

None of these

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

Increase the minority carrier current

Increase the majority carrier current

Raises the potential barrier

Lowers the potential barrier

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 to base

Holes move from base to emitter

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

4.9

9.8

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

4.9

9.8

142. 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

143. The energy band gap is maximum in

Insulators

Semiconductors

Superconductors

Metals

144. The thickness of the base is equal to

Mean of thickness of emitter and collector

Thickness of emitter

Thickness of collector

Very small as compared to the thickness of emitter and collector

145. The energy band gap is maximum in

Insulators

Superconductors

Semiconductors

Metals

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

Increase its electrical resistivity

Enable it to Telerate higher voltage

Increases its electrical conductivity

Increase its life

147. 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

AND

NAND

148. When NPN transistor is used as an amplifier

Electrons move from emitter to base

Electrons move from collector to base

Holes move from base to emitter

Electrons move from base to emitter

149. To use a transistor as an amplifier

No bias voltages are required

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

Both junctions are forward biased

Both junctions are reverse biased

150. A NAND gate has:

LOW inputs and a LOW output

HIGH inputs and a HIGH output

LOW inputs and a HIGH output

None of these

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

n-type semiconductor

p-type semiconductor

p-type conductor

n-type conductor

152. 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

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

Wide

Narrow

Infinity

Zero

154. Which logic gate is represented by following diagram?

EOR

NOR

AND

155. n-type semiconductor if formed

From pure Ge crystal

From pure Si crystal

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

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

156. Non-inverting amplifier circuits have

None of these

A very high input impedance

A low output impedance

A very low input impedance

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

Unit amplitude

Variable amplitude

Zero amplitude

Constant amplitude

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

Young’s modulus

Shear modulus

Bulk modulus

None of these

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

Superconductors

Insulators

Conductors

Semiconductors

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

161. Zener breakdown in a semiconductor diode occurs when

Reverse bias exceeds certain value

Forward bias exceeds certain value

Potential barrier is reduced to zero

Forward current exceeds certain value

162. A transistor consists of

Two PN-junctions

Three PN-junctions

One PN-junction

Four PN-junctions

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

Capacitor

Off switch

Inductor

On switch

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

Remains unchanged

Increases

Decreases

Decreases and then increases

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

mix

any of above

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

To A.C.

In reverse bias

In forward bias

None of these

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

None of these

Detector

Rectifier

Oscillator

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

The photo diodes

The switch

Solar cells

The light emitting diode

169. Symbol represents

XNOR gate

NOT gate

NAND gate

NOR gate

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

NOT gate

AND gate

XOR gate

OR gate

171. The least doped region in a transistor is

Collector

Base

Emitter

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

Gamma Rays

Electromagnetic Waves

Transverse Waves

x-rays

173. Transistor can be used as

Amplifier

Filter

Full wave rectifier

Half wave rectifier

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

Forward bias

Temperature

Doping density

Diode design

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

Holes move from emitter to base

Holes move from base to emitter

Holes move from emitter be base

Electrons move from base to collector

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

AND gate

NOT gate

NOR gate

OR gate

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

Collector

Base

Can be any of the above three

Emitter

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Malik TahirLast Updated: October 13, 2025

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