Class 12 Physics Ch-14 Semiconductor Devices Logic Gate MCQs Exam 2027

Topic 1: Semiconductor Physics

1. With the increase of temperature, the resistance of a semiconductor: [BSEB, 2022, 2025]

(A) Increases

(B) Decreases

(C) Remains unchanged

(D) Sometimes increases, sometimes decreases

2. The width of the forbidden energy gap in a semiconductor is approximately: [BSEB, 2024]

(A) 1 eV

(B) 10 eV

(C) 100 eV

(D) 0.01 eV

3. The value of the temperature coefficient of a semiconductor is: [BSEB, 2023]

(A) Positive

(B) Negative

(C) Zero

(D) Infinite

4. At absolute zero temperature, a semiconductor behaves as: [BSEB, 2014]

(A) A perfect conductor

(B) A perfect insulator

(C) A superconductor

(D) A semiconductor

5. The conductivity of a substance increases with temperature. That substance is:

(A) Metallic conductor

(B) Insulator

(C) Alloy

(D) Semiconductor

6. The cause of electrical conductivity in a semiconductor is:

(A) Electrons only

(B) Holes only

(C) Both electrons and holes

(D) Protons only

7. The band-gap in electron-volts for Germanium and Silicon are respectively: [BSEB, 2010]

(A) 0.7, 1.1

(B) 1.1, 0.7

(C) 1.1, 0

(D) 0.1, 1.1

8. The gap between the valence energy band and conduction energy band is called: [BSEB, 2011]

(A) Fermi band

(B) Band gap

(C) Valence band

(D) Conduction band

9. In a conducting material, between the valence band and the conduction band:

(A) There is a wide band gap

(B) There is a narrow band gap

(C) There is no empty space (overlap)

(D) None of these

10. A semiconductor is damaged by strong current due to: [BSEB, 2026]

(A) Lack of free electrons

(B) Excess of protons

(C) Heat generated by excess of electrons

(D) Excess of neutrons

Topic 2: p-type and n-type Semiconductors

11. The charge carriers in p-type semiconductors are: [BSEB, 2016, 2020]

(A) Electrons

(B) Holes

(C) Protons

(D) Neutrons

12. The main current carriers in n-type semiconductors are: [BSEB, 2011, 2015]

(A) Protons

(B) Holes

(C) $\alpha$-particles

(D) Electrons

13. The valency of a donor impurity atom is: [BSEB, 2021]

(A) 3

(B) 4

(C) 5

(D) 6

14. Which element is used as an impurity for p-type semiconductors? [BSEB, 2023]

(A) Boron

(B) Bismuth

(C) Arsenic

(D) Phosphorus

15. A p-type semiconductor is: [BSEB, 2021]

(A) Positively charged

(B) Negatively charged

(C) Uncharged (Neutral)

(D) Uncharged at absolute zero but charged at high temperatures

16. The process of adding impurities to semiconductors is called: [BSEB, 2018]

(A) Doping

(B) Ionization

(C) Discharge

(D) None of these

17. Majority charge carriers in a semiconductor will be electrons if the impurity is:

(A) Monovalent

(B) Divalent

(C) Trivalent

(D) Pentavalent

18. Adding a small amount of Arsenic to Silicon makes its conductivity: [BSEB, 2014]

(A) Increase

(B) Decrease

(C) Remain unchanged

(D) Become zero

19. Minority charge carriers in n-type semiconductors are: [BSEB, 2025]

(A) Electrons

(B) Holes

(C) Electrons and holes

(D) None of these

20. The valency of the impurity element to convert Germanium crystal into p-type semiconductor is: [BSEB, 2026]

(A) 2

(B) 3

(C) 4

(D) 5

Topic 3: P-N Junction and Diodes

21. A P-N junction diode is used as a: [BSEB, 2024]

(A) Amplifier

(B) Oscillator

(C) Modulator

(D) Rectifier

22. Zener Diode is mainly used as: [BSEB, 2022, 2026]

(A) Amplifier

(B) Oscillator

(C) Voltage Regulator

(D) Rectifier

23. The thickness of the depletion layer in a junction diode is: [BSEB, 2015]

(A) $10^{-6}$ m

(B) $10^{-3}$ m

(C) $10^{-10}$ m

(D) $10^{-2}$ m

24. In a full-wave rectifier, if the input frequency is 50 Hz, then output frequency will be: [BSEB, 2024]

(A) 25 Hz

(B) 50 Hz

(C) 100 Hz

(D) 200 Hz

25. In a half-wave rectifier, if the input frequency is 50 Hz, then output frequency will be: [BSEB, 2026]

(A) 25 Hz

(B) 100 Hz

(C) 0 Hz

(D) 50 Hz

26. When a p-n junction diode is in forward bias:

(A) The height of the potential barrier decreases

(B) The height of the potential barrier increases

(C) The thickness of the depletion layer increases

(D) The thickness of the depletion layer remains unchanged

27. When a p-n junction diode is in reverse bias:

(A) Electrons and holes move towards the depletion region

(B) Electrons and holes move away from the depletion region

28. When an L.E.D. is reverse biased:

(A) Light is emitted from it

(B) Light is not emitted from it

(C) Absorption of light occurs

(D) None of these

29. To use junction diodes as a full-wave rectifier, we need:

(A) One diode

(B) Two diodes

(C) Three diodes

(D) Four diodes

30. The function of a rectifier is: [BSEB, 2019]

(A) To convert AC to DC

(B) To convert DC to AC

(C) To convert low voltage to high

(D) None of these

Topic 4: Transistors

31. The correct relationship between transistor parameters $\alpha$ and $\beta$ is: [BSEB, 2018]

(A) $\alpha = \frac{\beta}{\beta – 1}$

(B) $\beta = \frac{\alpha}{1 – \alpha}$

(C) $\alpha = \frac{\beta + 1}{\beta}$

(D) $\beta = \frac{\alpha + 1}{\alpha}$

32. In the operation of an n-p-n transistor, the relation between $I_e$, $I_b$, and $I_c$ is:

(A) $I_c = I_e – I_b$

(B) $I_b = I_e + I_c$

(C) $I_e = I_c – I_b$

(D) $I_b = I_e = I_c$

33. The unit of the amplification factor of a transistor is: [BSEB, 2023]

(A) Volt

(B) Ampere

(C) Ohm

(D) No unit

34. The current gain of a transistor is defined as ($\alpha$):

(A) $\alpha = I_c / I_e$

(B) $\alpha = I_e / I_c$

(C) $\alpha = I_c / I_b$

(D) $\alpha = I_b / I_c$

35. In common emitter configuration, the current gain is ($\beta$):

(A) $\beta = I_c / I_b$

(B) $\beta = I_e / I_b$

(C) $\beta = I_c / I_e$

(D) $\beta = I_e / I_c$

36. The region in which a transistor acts as a switch is: [BSEB, 2021]

(A) Active region

(B) Cut-off and Saturation region

(C) Saturation region only

(D) Cut-off region only

37. In a transistor, the concentration of impurities is minimum in: [BSEB, 2026]

(A) Collector

(B) Emitter

(C) Base

(D) All three regions

38. The device used to increase input voltage/current is called: [BSEB, 2024]

(A) Oscillator

(B) Amplifier

(C) Diode

(D) Rectifier

39. To make a NOT gate, we use:

(A) n-p-n transistor with common emitter

(B) n-p-n transistor with common base

(C) p-n-p transistor with common emitter

(D) p-n-p transistor with common base

40. If current constants of a transistor are $\alpha$ and $\beta$, then: [BSEB, 2018]

(A) $\alpha \cdot \beta = 1$

(B) $\beta > 1, \alpha < 1$

(C) $\alpha = \beta$

(D) $\beta < 1, \alpha > 1$

Topic 5: Logic Gates

41. The Boolean expression for NAND gate is: [BSEB, 2017, 2019, 2025]

(A) $\overline{A \cdot B} = Y$

(B) $A \cdot B = Y$

(C) $\overline{A + B} = Y$

(D) $A + B = Y$

42. The Boolean expression for NOR gate is: [BSEB, 2016, 2021, 2026]

(A) $A + B = Y$

(B) $A \cdot B = Y$

(C) $\overline{A + B} = Y$

(D) $\overline{A \cdot B} = Y$

43. The Boolean expression for OR gate is: [BSEB, 2013]

(A) $A + B = Y$

(B) $A \cdot B = Y$

(C) $\overline{A} = A$

(D) $C = AB$

44. The Boolean expression for AND gate is:

(A) $A + B = Y$

(B) $\overline{A \cdot B} = Y$

(C) $A \cdot B = Y$

(D) $\overline{A + B} = Y$

45. Which of the following is a Universal Logic Gate? [BSEB, 2023]

(A) OR

(B) AND

(C) NOT

(D) NAND

46. Which of the following is correct for Basic Gates? [BSEB, 2021]

(A) AND, OR, NOT

(B) AND, OR

(C) NAND, NOR

(D) OR, NOT

47. If the output ($Y$) of a logic gate is obtained by the product of its inputs ($A, B$), the gate is: [BSEB, 2024]

(A) AND

(B) OR

(C) NOR

(D) NOT

48. The truth table (0,0 → 1; 0,1 → 1; 1,0 → 1; 1,1 → 0) belongs to which gate:

(A) NAND

(B) AND

(C) OR

(D) NOR

49. If output 1 is obtained when both inputs of a logic gate are at 0, the gate is:

(A) AND

(B) OR

(C) NOT

(D) NOR

50. Which logic gate gives the same output even when inputs are different? [BSEB, 2025]

(A) OR gate

(B) AND gate

(C) NOT gate

(D) XOR gate

Topic 6: Number Systems

51. Binary of decimal number 25 is: [BSEB, 2020, 2023]

(A) $(1100)_2$

(B) $(1001)_2$

(C) $(11001)_2$

(D) $(11101)_2$

52. Decimal 27 is equivalent to which binary number? [BSEB, 2024]

(A) $(10011)_2$

(B) $(10111)_2$

(C) $(11001)_2$

(D) $(11011)_2$

53. Binary of decimal number (8)₁₀ is: [BSEB, 2022]

(A) $(1000)_2$

(B) $(1001)_2$

(C) $(111)_2$

(D) $(110)_2$

54. Decimal number for binary (1001)₂ is: [BSEB, 2021]

(A) $(12)_{10}$

(B) $(18)_{10}$

(C) $(9)_{10}$

(D) $(25)_{10}$

55. Value of binary 10101 in decimal system is: [BSEB, 2018]

(A) 31

(B) 21

(C) 11

(D) 3

56. Binary equivalent of 15 is: [BSEB, 2018]

(A) $(10111)_2$

(B) $(10010)_2$

(C) $(1111)_2$

(D) $(111000)_2$

57. Binary number 111 represents:

(A) One

(B) Three

(C) Seven

(D) One hundred eleven

58. Which of the following is correct? [BSEB, 2021]

(A) $(1100)_2 = (12)_{10}$

(B) $(1001)_2 = (12)_{10}$

(C) $(1111)_2 = (12)_{10}$

(D) $(1011)_2 = (12)_{10}$

59. Binary of decimal number 12 will be: [BSEB, 2021]

(A) $(1100)_2$

(B) $(1001)_2$

(C) $(1110)_2$

(D) $(1010)_2$

60. Decimal equivalent of binary (110)₂ is:

(A) 4

(B) 6

(C) 8

(D) 10

Topic 7: Communication Systems

61. The value of modulation index in amplitude modulation is always: [BSEB, 2021, 2024]

(A) 0

(B) Between 1 and 100

(C) Between 0 and 1

(D) Always infinite

62. UHF (Ultra High Frequency) waves are usually transmitted as: [BSEB, 2022]

(A) Ground waves

(B) Sky waves

(C) Space waves

(D) Ionospheric waves

63. The reverse process of modulation is called: [BSEB, 2021]

(A) Demodulation

(B) Amplification

(C) Transmission

(D) Reception

64. Frequency range used for TV transmission is: [BSEB, 2021, 2025]

(A) 30 – 300 Hz

(B) 30 – 300 kHz

(C) 30 – 300 MHz

(D) 30 – 300 GHz

65. The principle of Optical Fibre is: [BSEB, 2022, 2024]

(A) Refraction

(B) Diffraction

(C) Total Internal Reflection (TIR)

(D) Scattering

66. Reflection of radio waves occurs from which layer of the sky? [BSEB, 2023]

(A) Ionosphere

(B) Troposphere

(C) Stratosphere

(D) Ozonosphere

67. Which frequency is suitable for beyond-the-horizon communication using sky waves? [BSEB, 2022]

(A) 10 kHz

(B) 10 MHz

(C) 1 GHz

(D) 1000 GHz

68. Which of the following is not a part of a communication system? [BSEB, 2024]

(A) Transmitter

(B) Transmission Channel

(C) Receiver

(D) Energy

69. Which unit is correct for measuring Attenuation? [BSEB, 2021]

(A) Decibel

(B) Ohm

(C) Ampere

(D) Volt

70. Sky Wave propagation is based on:

(A) Reflection by ionosphere

(B) Absorption by ionosphere

(C) Transmission through ionosphere

(D) None of these

71. Maximum height of an A.M. wave is 15 V and minimum is 3 V. Modulation index will be:

(A) 2/3

(B) 1/2

(C) 1/4

(D) 3/5

72. FAX stands for: [BSEB, 2019]

(A) Full Access Transmission

(B) Facsimile Telephony

(C) Factual Auto Exchange

(D) Facsimile Telegraphy

73. How many types of modulation are there?

(A) 2

(B) 3

(C) 4

(D) 5

74. The device used for modulation is called:

(A) Modem

(B) Demodulator

(C) Oscillator

(D) Amplifier

75. The height of a communication satellite from the Earth’s surface is approximately:

(A) 3600 km

(B) 36000 km

(C) 1000 km

(D) 500 km

Topic 8: Applications & Miscellaneous

76. Solar cell panels are used in: [BSEB, 2023]

(A) Artificial satellites

(B) On the moon

(C) On Mars

(D) Nowhere

77. The device that converts solar energy into electrical energy is: [BSEB, 2024]

(A) Solar cell

(B) Dry cell

(C) Storage cell

(D) Button cell

78. Reverse biased diode is: [BSEB, 2025]

(A) Zener diode

(B) LED

(C) Photodiode

(D) Both ‘A’ and ‘C’

79. Which of the following is charge-less? [BSEB, 2021, 2024]

(A) Alpha particle

(B) Beta particle

(C) Photon particle

(D) Proton

80. The time in which the quantity of a radioactive substance becomes half is called: [BSEB, 2021]

(A) Average life

(B) Half-life

(C) Time period

(D) Decay constant

81. Photodiode is used in:

(A) Detection of light signals

(B) Rectifier

(C) Amplifier

(D) Oscillator

82. Most light emitted by GaP junction is:

(A) Red and Green

(B) Red and Yellow

(C) Red and Violet

(D) None of these

83. Efficiency of a solar cell is approximately:

(A) 10% – 15%

(B) 50%

(C) 80%

(D) 100%

84. A semiconductor is cooled from T₁ K to T₂ K, its resistance: [BSEB, 2018]

(A) Increases

(B) Decreases

(C) Remains constant

(D) First increases then decreases

85. Silicon is a semiconductor. Adding Boron (B) to it will make it:

(A) p-type

(B) n-type

(C) Metal

(D) Insulator

86. Conduction bands are partially empty in:

(A) Insulators

(B) Semiconductors

(C) Metals

(D) None of these

87. Electrical conduction in extrinsic semiconductors is possible:

(A) At high temperatures

(B) At every temperature

(C) At 36°C

(D) At 98°F

88. Pure Germanium is obtained when mixed with:

(A) Indium

(B) Gold

(C) Copper

(D) Arsenic

89. The device that produces direct current when alternating potential is applied is:

(A) Rectifier

(B) Transformer

(C) Oscillator

(D) Filter

90. To make p-type semiconductor, Germanium is doped with: [BSEB, 2018]

(A) Gallium

(B) Boron

(C) Aluminum

(D) Phosphorus

91. The impurity atom added to pure silicon to make n-type semiconductor is:

(A) Phosphorus

(B) Boron

(C) Antimony

(D) Aluminum

92. The interval between the valence energy band and conduction energy band is called:

(A) Fermi band

(B) Band gap

(C) Valence band

(D) Conduction band

93. The behavior of a pure semiconductor at absolute zero temperature is:

(A) Like an insulator

(B) Like a superconductor

(C) Like an n-type semiconductor

(D) Like a metallic conductor

94. The width of P-N junction in reverse bias:

(A) Increases

(B) Decreases

(C) Remains same

(D) Becomes zero

95. Photodiode works on the principle of:

(A) Photoelectric effect

(B) Thermionic emission

(C) Dispersion

(D) Interference

96. The value of current gain $\beta$ in a transistor is generally:

(A) Less than 1

(B) Between 20 and 500

(C) Zero

(D) Infinite

97. The relation $\alpha = \frac{\beta}{1+\beta}$ is for which configuration?

(A) CB configuration

(B) CE configuration

(C) CC configuration

(D) All of these

98. The value of current gain $\alpha$ in common base (CB) configuration is:

(A) Always less than 1

(B) Always more than 1

(C) Equal to 1

(D) Zero

99. A transistor works as an amplifier when it is in:

(A) Active region

(B) Saturation region

(C) Cut-off region

(D) None of these

100. Voltage gain for a CE amplifier depends on:

(A) Load resistance

(B) Input resistance

(C) $\beta$

(D) All of the above

101. Why is the Base region made very thin in a transistor?

(A) To reduce recombination

(B) To increase current

(C) To reduce resistance

(D) To increase voltage

102. The size of the Collector region is larger than the Emitter:

(A) For heat dissipation

(B) To reduce current

(C) To increase doping

(D) For aesthetics

103. A transistor can be used as:

(A) A switch

(B) An amplifier

(C) An oscillator

(D) All of these

104. The circuit used to reduce Ripple in a rectifier circuit is:

(A) Filter circuit

(B) Tank circuit

(C) Logic circuit

(D) None of these

105. Maximum efficiency of a rectifier is:

(A) 40.6% in half-wave

(B) 81.2% in full-wave

(C) Both ‘A’ and ‘B’

(D) None of these

106. Truth table (0,0 → 0; 0,1 → 1; 1,0 → 1; 1,1 → 1) represents:

(A) OR gate

(B) AND gate

(C) NAND gate

(D) NOR gate

107. What else is the NOT gate called?

(A) Inverter

(B) Accumulator

(C) Divider

(D) Adder

108. Boolean expression for XOR gate is:

(A) $Y = A\bar{B} + \bar{A}B$

(B) $Y = A + B$

(C) $Y = A \cdot B$

(D) $Y = \overline{A+B}$

109. Logic gates are based on:

(A) Boolean Algebra

(B) Trigonometry

(C) Calculus

(D) Geometry

110. NAND gate means:

(A) NOT + AND

(B) NOT + OR

(C) NOT + XOR

(D) Only AND

111. NOR gate means:

(A) NOT + OR

(B) NOT + AND

(C) NOT + NOT

(D) OR + AND

112. Which gate can also be called ‘Equality Gate’?

(A) XNOR

(B) XOR

(C) AND

(D) OR

113. How many conditions are possible for a 3-input AND gate?

(A) 4

(B) 8

(C) 16

(D) 2

114. In logic gates, ‘1’ represents:

(A) ON / High Voltage

(B) OFF / Low Voltage

(C) Zero

(D) Uncertain

115. In logic gates, ‘0’ represents:

(A) Low Voltage / OFF

(B) High Voltage / ON

(C) One

(D) Uncertain

116. Which layer is lowest among the ionosphere layers?

(A) D-layer

(B) E-layer

(C) F-layer

(D) G-layer

117. Noise in communication system means:

(A) Unwanted signal

(B) Sweet music

(C) Sender’s voice

(D) None of these

118. Digital signals use:

(A) 0 and 1

(B) Digits from 0 to 9

(C) Only 1

(D) All real numbers

119. In Analog signal, change occurs:

(A) Continuously with time

(B) In steps

(C) Between only two values

(D) Never

120. Function of a Repeater is:

(A) To increase signal range

(B) To stop the signal

(C) To decrease signal

(D) To delete data

121. Why is modulation needed?

(A) To reduce antenna length

(B) To increase signal power

(C) To prevent signal mixing

(D) All of the above

122. Where is demodulation done?

(A) At the Receiver

(B) At the Transmitter

(C) On the channel

(D) At the antenna

123. Protocol used in Internet is:

(A) TCP/IP

(B) HTML

(C) WWW

(D) FAX

124. Full form of ‘WWW’ is:

(A) World Wide Web

(B) World Whole Web

(C) Wide World Web

(D) World Wide Wire

125. Refractive index of Core in optical fiber relative to Cladding is:

(A) Higher

(B) Lower

(C) Equal

(D) Zero

126. Decimal value of binary (11001)₂ is:

(A) 25

(B) 27

(C) 21

(D) 19

127. Binary of decimal 10 is:

(A) (1010)₂

(B) (1100)₂

(C) (1001)₂

(D) (1111)₂

128. Main material used in solar cells is:

(A) Silicon

(B) Copper

(C) Iron

(D) Aluminum

129. Solar cell is not used in:

(A) Cooking food directly

(B) Artificial satellites

(C) Calculators

(D) Wristwatches

130. Used as a ‘filter’ in rectifiers:

(A) Capacitor

(B) Resistor

(C) Diode

(D) Switch

131. LED (Light Emitting Diode) works in which bias?

(A) Forward bias

(B) Reverse bias

(C) Both

(D) Neither

132. Photodiode works in which bias?

(A) Reverse bias

(B) Forward bias

(C) Both

(D) Zero bias

133. Zener voltage of Zener diode depends on:

(A) Doping concentration

(B) Temperature

(C) Both ‘A’ and ‘B’

(D) Only current

134. Integrated Circuits (IC) are made of:

(A) Semiconductors

(B) Conductors

(C) Insulators

(D) Plastic

135. Who invented the transistor?

(A) Bardeen, Brattain, and Shockley

(B) Newton

(C) Einstein

(D) Faraday

136. Binary of decimal 19 is:

(A) (10011)₂

(B) (11001)₂

(C) (10101)₂

(D) (11111)₂

137. Binary sum 1 + 1 equals:

(A) 10 (0 with carry 1)

(B) 2

(C) 0

(D) 1

138. Property of LASER rays is:

(A) Monochromatic

(B) Highly coherent

(C) Highly directional

(D) All of the above

139. Cause of light loss in optical fiber is:

(A) Absorption and Scattering

(B) Diffraction

(C) Refraction

(D) None of these

140. Source of energy used in communication satellites is:

(A) Solar cells

(B) Diesel engine

(C) Nuclear reactor

(D) Battery only

141. What happens if modulation index (m) is greater than 1?

(A) Distortion

(B) Clear voice

(C) No effect

(D) Signal stops

142. Used for long-distance radio broadcasting:

(A) Sky waves

(B) Ground waves

(C) Space waves

(D) None of these

143. Process of converting digital data into analog signal is:

(A) Modulation

(B) Demodulation

(C) Amplification

(D) Noise

144. Correct relation between currents $I_e, I_b$, and $I_c$ in a transistor is:

(A) $I_e = I_b + I_c$

(B) $I_b = I_e + I_c$

(C) $I_c = I_e + I_b$

(D) $I_e = I_b – I_c$

145. Resistance of a junction diode in forward bias is:

(A) Very low

(B) Very high

(C) Infinite

(D) Zero

146. Resistance of a junction diode in reverse bias is:

(A) Very high

(B) Very low

(C) Zero

(D) Constant

147. Direction of internal electric field built at P-N junction is:

(A) n to p

(B) p to n

(C) Upwards

(D) Downwards

148. Which diode is used as a voltage stabilizer?

(A) Zener diode

(B) Normal diode

(C) Tunnel diode

(D) Gunn diode

149. What does the truth table of a logic gate show?

(A) Relation between input and output

(B) Weight of the gate

(C) Temperature of the gate

(D) Price of the gate

150. What is the basis of semiconductor electronics?

(A) P-N Junction

(B) Metal wire

(C) Vacuum tube

(D) Rubber