Class 12 Physics Ch-15 Communication Systems MCQs Exam 2027

Topic 1: Communication Systems

1. The example of a broadcast mode of communication is: [BSEB, 2026]

   (A) Radio

   (B) Telephone

   (C) Television

   (D) Both (A) and (C)

2. In a communication system, a repeater is: [BSEB, 2026]

   (A) A receiver

   (B) A transmitter

   (C) Combination of receiver and transmitter

   (D) None of these

3. ‘World Wide Web’ (WWW) was invented by: [BSEB, 2026]

   (A) Tim Berners-Lee

   (B) John Logie Baird

   (C) Alexander Bain

   (D) G. Marconi

4. The frequency range used for TV transmission is: [BSEB, 2019, 21, 23, 25]

   (A) 30-300 Hz

   (B) 30-300 KHz

   (C) 30-300 MHz

   (D) 30-300 GHz

5. ‘FAX’ stands for: [BSEB, 2018 (A)]

   (A) Full Access Transmission

   (B) Facsimile Telegraphy

   (C) Factual Auto Access

   (D) Feed Auto Exchange

6. The distance of a communication satellite from the Earth’s surface is: [BSEB, 2024 (A)]

   (A) 36000 km

   (B) 36000 miles

   (C) 3600 km

   (D) 3600 miles

7. A device that converts one form of energy into another is called: [BSEB, 2022]

   (A) Converter

   (B) Inverter

   (C) Transducer

   (D) Transformer

8. Which of the following units is correct for measuring Attenuation? [BSEB, 2021, 24]

   (A) Decibel (dB)

   (B) Ohm

   (C) Ampere

   (D) Volt

9. For long-distance radio broadcasting, which of the following is mainly used? [BSEB, 2015]

   (A) Ground waves

   (B) Line of sight waves

   (C) Ionospheric waves

   (D) Satellite communication

10. Communication by Sky Wave is based on: [BSEB, 2009, 18, 22]

    (A) Reflection by Ionosphere

    (B) Absorption by Ionosphere

    (C) Transmission through Ionosphere

    (D) None of these

11. A device that performs both modulation and demodulation is: [BSEB, 2024]

    (A) LASER

    (B) RADAR

    (C) Modem

    (D) Fax

12. Frequencies in the UHF range normally propagate by: [BSEB, 2016]

    (A) Ground waves

    (B) Sky waves

    (C) Surface waves

    (D) Space waves

13. The height of a TV transmission tower is 245 m. The maximum distance up to which the broadcast can reach is: [BSEB, 2017, 19]

    (A) 245 m

    (B) 245 km

    (C) 56 km

    (D) 112 km

14. Which part of electromagnetic waves is used in satellite communication? [BSEB, 2014]

    (A) Light waves

    (B) Radio waves

    (C) Gamma rays

    (D) Microwaves

15. Space communication involves: [BSEB, 2013]

    (A) Reflection

    (B) Refraction

    (C) Diffraction and Interference

    (D) All of these

16. The time period of a communication satellite is: [BSEB, 2020]

    (A) 1 year

    (B) 24 hours

    (C) 27.3 hours

    (D) Not fixed

17. The device used to detect the position, distance, and direction of far objects using radio waves: [BSEB, 2017]

    (A) LASER

    (B) RADAR

    (C) MASER

    (D) None of these

18. In Radio Telegraphy, what is transmitted? [BSEB, 2012]

    (A) Pictures

    (B) Sound

    (C) Information via codes

    (D) Physical position of objects

19. For ground waves, the frequency should be: [BSEB, 2018 (C)]

    (A) More than $10^6$ Hz

    (B) Less than $10^6$ Hz

    (C) More than $10^{10}$ Hz

    (D) None of these

20. The height of the ionosphere from the Earth’s surface is approximately: [BSEB, 2011]

    (A) 2 km to 10 km

    (B) 10 km to 50 km

    (C) 65 km to 400 km

    (D) Above 1000 km

21. A device that increases the power of a signal is: [BSEB, 2024]

    (A) Amplifier

    (B) Rectifier

    (C) Modulator

    (D) Transmitter

22. For a radio signal of frequency 10 MHz, the required antenna length should be: [BSEB, 2016]

    (A) 40 m

    (B) 30 m

    (C) 20 m

    (D) 10 m

23. The frequency of Microwaves is: [BSEB, 2019]

    (A) Greater than radio waves

    (B) Less than radio waves

    (C) Greater than light waves

    (D) None of these

24. The velocity of radio waves in vacuum is: [BSEB, 2010]

    (A) $3 \times 10^8$ m/s

    (B) $3 \times 10^{10}$ m/s

    (C) $3 \times 10^6$ m/s

    (D) Zero

25. A microphone converts: [BSEB, 2022]

    (A) Sound into electrical signals

    (B) Electrical into sound signals

    (C) Light into electrical signals

    (D) None of these

26. Which of the following is NOT an essential element of a communication system? [BSEB, 2014]

    (A) Transmitter

    (B) Medium

    (C) Receiver

    (D) Luminance

27. The full form of WWW is: [BSEB, 2026]

    (A) World Wide Web

    (B) World Whole Web

    (C) Wide World Web

    (D) World White Web

28. The main function of a Modem is: [BSEB, 2024]

    (A) Only modulation

    (B) Only demodulation

    (C) Both modulation and demodulation

    (D) Amplification

29. In a communication system, Noise is most likely to be added in: [BSEB, 2018]

    (A) Transmitter

    (B) Channel (Medium)

    (C) Receiver

    (D) None of these

30. The protocol used for the Internet is: [BSEB, 2026]

    (A) TCP/IP

    (B) HTTP

    (C) FTP

    (D) All of these

Topic 2: Modulation

31. How many types of modulation are there? [BSEB, 2017, 21]

    (A) 2 types

    (B) 3 types

    (C) 4 types

    (D) 5 types

32. The value of the Amplitude Modulation Index lies: [BSEB, 2015, 19, 21]

    (A) Always 0

    (B) Between 1 and $\infty$

    (C) Between 0 and 1

    (D) Always $\infty$

33. The process of superimposing information on a carrier wave is: [BSEB, 2022]

    (A) Modulation

    (B) Demodulation

    (C) Amplification

    (D) Rectification

34. The process opposite to modulation is called: [BSEB, 2021]

    (A) Demodulation

    (B) Transmission

    (C) Remote sensing

    (D) Fax

35. When the modulation index $(\mu)$ in AM exceeds 1, it causes: [BSEB, 2010, 21]

    (A) Distortion

    (B) Better clarity

    (C) No effect

    (D) Efficiency becomes zero

36. In FM (Frequency Modulation), what changes? [BSEB, 2016]

    (A) Carrier amplitude

    (B) Carrier frequency

    (C) Carrier phase

    (D) All of these

37. Modulation is necessary for: [BSEB, 2013]

    (A) Reducing antenna length

    (B) Reducing energy loss

    (C) Sending signals to long distances

    (D) All of these

38. Frequency Modulation (FM) is superior to Amplitude Modulation (AM) because: [BSEB, 2015]

    (A) It has less noise

    (B) It is cheaper

    (C) The circuit is simple

    (D) It requires less bandwidth

39. Which of the following is NOT a type of modulation? [BSEB, 2020]

    (A) AM

    (B) FM

    (C) PM

    (D) NM

40. Modulation is a device that:

    (A) Encodes information on a carrier wave

    (B) Separates two frequencies

    (C) Extracts information from carrier

    (D) Amplifies sound signal

Topic 3: Optical Fibre

41. Optical Fibre works on the principle of: [BSEB, 2016, 21, 24]

    (A) Refraction

    (B) Scattering

    (C) Diffraction

    (D) Total Internal Reflection

42. Which type of waves are used in Fiber Optic communication? [BSEB, 2025]

    (A) Sound waves

    (B) Light waves (EM waves)

    (C) Seismic waves

    (D) Mechanical waves

43. The core of an optical fibre is made of: [BSEB, 2019]

    (A) High-quality glass or plastic

    (B) Copper

    (C) Iron

    (D) Aluminum

44. The refractive index of Cladding compared to Core is: [BSEB, 2018]

    (A) Greater

    (B) Less

    (C) Equal

    (D) Zero

45. An optical fibre is a: [BSEB, 2023]

    (A) Transmission line

    (B) Waveguide

    (C) Both (A) and (B)

    (D) None of these

46. For optical fibres, the general value of the Critical Angle is: [BSEB, 2016]

    (A) $17^\circ$

    (B) $20^\circ$

    (C) $59^\circ$

    (D) $77^\circ$

47. Attenuation of light in optical fibre is mainly due to: [BSEB, 2022]

    (A) Absorption and Scattering

    (B) Refraction

    (C) Diffraction

    (D) Interference

48. What is used in Endoscopy? [BSEB, 2015]

    (A) LASER

    (B) Optical Fibre

    (C) X-ray

    (D) RADAR

49. The efficiency of optical fibre communication depends on: [BSEB, 2024]

    (A) Core diameter

    (B) Frequency of light

    (C) Both (A) and (B)

    (D) None of these

50. Step Index and Graded Index are types of: [BSEB, 2021]

    (A) Modulation

    (B) Fibre structure

    (C) Antenna

    (D) None of these

Topic 4: Semiconductor Electronics

51. The majority charge carriers in $n$-type semiconductors are: [BSEB, 2016, 2022]

    (A) Electrons

    (B) Holes

    (C) Protons

    (D) $\alpha$-particles

52. The majority charge carriers in $p$-type semiconductors are: [BSEB, 2022]

    (A) Electrons

    (B) Holes

    (C) Photons

    (D) Protons

53. A Zener Diode is mainly used as: [BSEB, 2023]

    (A) Amplifier

    (B) Voltage Regulator

    (C) Oscillator

    (D) Rectifier

54. A device that converts solar energy into electrical energy is: [BSEB, 2023]

    (A) Solar cell

    (B) Dry cell

    (C) Button cell

    (D) Storage cell

55. Electrical conductivity in semiconductors is due to: [BSEB, 2024]

    (A) Only electrons

    (B) Only holes

    (C) Both electrons and holes

    (D) Protons

56. The valency of a Donor Impurity atom is: [BSEB, 2017, 21]

    (A) 3

    (B) 4

    (C) 5

    (D) 6

57. A $p-n$ junction diode is used as a: [BSEB, 2015, 20]

    (A) Rectifier

    (B) Amplifier

    (C) Modulator

    (D) Oscillator

58. With the increase in temperature, the resistance of a semiconductor: [BSEB, 2015, 19]

    (A) Increases

    (B) Decreases

    (C) Remains constant

    (D) First increases then decreases

59. For a $p$-type semiconductor, the impurity added is: [BSEB, 2024]

    (A) Phosphorus

    (B) Antimony

    (C) Indium / Aluminum

    (D) Arsenic

60. The forbidden energy gap in pure semiconductors is approximately: [BSEB, 2018]

    (A) 1 eV

    (B) 10 eV

    (C) 100 eV

    (D) Zero

61. An $n$-type semiconductor is electrically: [BSEB, 2020]

    (A) Negatively charged

    (B) Positively charged

    (C) Neutral

    (D) None of these

62. In a transistor, the doping of the Base is: [BSEB, 2021]

    (A) Very low

    (B) Very high

    (C) Equal to Collector

    (D) Equal to Emitter

63. For half-wave rectification, what is the output frequency for 50 Hz input? [BSEB, 2022]

    (A) 25 Hz

    (B) 50 Hz

    (C) 100 Hz

    (D) 200 Hz

64. For full-wave rectification, what is the output frequency for 50 Hz input? [BSEB, 2022]

    (A) 50 Hz

    (B) 100 Hz

    (C) 200 Hz

    (D) 25 Hz

65. Integrated Circuits (IC) are made using: [BSEB, 2016]

    (A) Copper

    (B) Aluminum

    (C) Silicon

    (D) Iron

66. The relation between current gains $\alpha$ and $\beta$ of a transistor is: [BSEB, 2021]

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

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

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

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

67. The width of the depletion layer in a $p-n$ junction in reverse bias: [BSEB, 2023]

    (A) Increases

    (B) Decreases

    (C) Remains same

    (D) Becomes zero

68. An LED emits light when it is: [BSEB, 2024]

    (A) Forward biased

    (B) Reverse biased

    (C) Unbiased

    (D) None of these

69. A Photo Diode is used for: [BSEB, 2017]

    (A) Detecting light

    (B) Amplification

    (C) Voltage regulation

    (D) None of these

70. The current relationship in an $n-p-n$ transistor is: [BSEB, 2020]

    (A) $I_E = I_B + I_C$

    (B) $I_C = I_E + I_B$

    (C) $I_B = I_E + I_C$

    (D) None of these

71. In a transistor, the size of the Collector compared to Emitter is: [BSEB, 2022]

    (A) Larger

    (B) Smaller

    (C) Equal

    (D) Very small

72. The valency of an Acceptor Impurity is: [BSEB, 2021]

    (A) 3

    (B) 4

    (C) 5

    (D) 2

73. At absolute zero temperature, a pure semiconductor behaves as: [BSEB, 2018]

    (A) Conductor

    (B) Perfect insulator

    (C) Superconductor

    (D) Semiconductor

74. The energy gap of Silicon is: [BSEB, 2019]

    (A) 1.1 eV

    (B) 0.7 eV

    (C) 5.0 eV

    (D) 0.1 eV

75. The energy gap of Germanium is: [BSEB, 2019]

    (A) 1.1 eV

    (B) 0.7 eV

    (C) 0.3 eV

    (D) 1.5 eV

76. The function of a filter in a rectifier circuit is: [BSEB, 2024]

    (A) Convert AC to DC

    (B) Remove ripples from waves

    (C) Increase voltage

    (D) Increase current

77. The most suitable material for making solar cells is: [BSEB, 2023]

    (A) Silicon (Si)

    (B) Copper (Cu)

    (C) Iron (Fe)

    (D) Gold (Au)

78. Zener Breakdown occurs when: [BSEB, 2016]

    (A) Doping is high

    (B) Doping is low

    (C) No doping

    (D) Temp is low

79. Current flow in semiconductors happens by: [BSEB, 2025]

    (A) Drift

    (B) Diffusion

    (C) Both (A) and (B)

    (D) Only protons

80. How many $p-n$ junctions are in a transistor?

    (A) 1

    (B) 2

    (C) 3

    (D) 4

Topic 5: Logic Gates

81. The Boolean expression for a NOR gate is: [BSEB, 2018, 2021]

    (A) $A \cdot B = Y$

    (B) $A + B = Y$

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

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

82. The Boolean expression for a NAND gate is: [BSEB, 2015, 2024]

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

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

    (C) $A \cdot B = Y$

    (D) $A + B = Y$

83. The Boolean expression for an OR gate is: [BSEB, 2016, 2022]

    (A) $A + B = Y$

    (B) $A \cdot B = Y$

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

    (D) $C = AB$

84. What is used to make a NOT gate? [BSEB, 2021]

    (A) n-p-n transistor (CE mode)

    (B) p-n-p transistor (CB mode)

    (C) Diode

    (D) None of these

85. Possible values in a Digital Signal are: [BSEB, 2014]

    (A) 0 and 1

    (B) All values

    (C) 0 to 9

    (D) Infinite values

86. The Boolean expression for an AND gate is: [BSEB, 2019, 23]

    (A) $A + B = Y$

    (B) $A \cdot B = Y$

    (C) $\bar{A} = Y$

    (D) $A \oplus B = Y$

87. Which of the following is a Universal Gate? [BSEB, 2020, 24]

    (A) AND

    (B) OR

    (C) NAND

    (D) NOT

88. Which gate is also called an ‘Inverter’? [BSEB, 2025]

    (A) AND

    (B) OR

    (C) NOT

    (D) NAND

[Image showing symbols and truth tables for AND, OR, NOT, NAND, and NOR gates]

89. In Boolean algebra, $A + 1$ is equal to: [BSEB, 2022]

    (A) 1

    (B) A

    (C) 0

    (D) $\bar{A}$

90. In Boolean algebra, $A \cdot A$ is equal to: [BSEB, 2021]

    (A) A

    (B) 1

    (C) 0

    (D) $A^2$

91. Binary addition $1 + 1$ equals: [BSEB, 2018]

    (A) 2

    (B) 10 (0 with carry 1)

    (C) 1

    (D) 0

92. The Boolean expression for an XOR gate is: [BSEB, 2016]

    (A) $Y = A \oplus B$

    (B) $Y = A + B$

    (C) $Y = A \cdot B$

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

93. A Logic Gate is a: [BSEB, 2011]

    (A) Digital circuit

    (B) Switch

    (C) Type of capacitor

    (D) None of these

94. The Boolean expression $\overline{A \cdot B} = Y$ represents:

    (A) NAND gate

    (B) NOR gate

    (C) AND gate

    (D) OR gate

95. The Boolean expression $A+0$ equals:

    (A) A

    (B) 0

    (C) 1

    (D) $\bar{A}$

Topic 6: Number Systems

96. The binary equivalent of decimal number $(8)_{10}$ is: [BSEB, 2023]

    (A) $(1000)_2$

    (B) $(1001)_2$

    (C) $(111)_2$

    (D) $(1010)_2$

97. The binary equivalent of decimal number 25 is: [BSEB, 2016, 20]

    (A) $(11001)_2$

    (B) $(10101)_2$

    (C) $(11011)_2$

    (D) $(11101)_2$

98. The decimal value of binary number $(111)_2$ is: [BSEB, 2020]

    (A) 7

    (B) 5

    (C) 3

    (D) 1

99. The decimal value of binary number $(1001)_2$ is: [BSEB, 2021]

    (A) 12

    (B) 18

    (C) 9

    (D) 7

100. The binary equivalent of decimal number $(15)_{10}$ is: [BSEB, 2018, 2021]

     (A) $(1100)_2$

     (B) $(1001)_2$

     (C) $(1111)_2$

     (D) $(1101)_2$

101. Binary equivalent of decimal 12: [BSEB, 2017]

     (A) $(1100)_2$

     (B) $(1010)_2$

     (C) $(1111)_2$

     (D) $(1000)_2$

102. Binary equivalent of decimal 10: [BSEB, 2024]

     (A) $(1010)_2$

     (B) $(1100)_2$

     (C) $(1001)_2$

     (D) $(1111)_2$

103. Decimal value of binary $(1101)_2$: [BSEB, 2015]

     (A) 11

     (B) 13

     (C) 15

     (D) 17

104. Binary equivalent of decimal 6: [BSEB, 2022]

     (A) $(110)_2$

     (B) $(101)_2$

     (C) $(111)_2$

     (D) $(100)_2$

105. How many bits are in a Byte? [BSEB, 2013]

     (A) 4

     (B) 8

     (C) 16

     (D) 32

Topic 7: Miscellaneous & Recent Patterns

106. Remote controls use: [BSEB, 2024]

     (A) Infrared rays

     (B) Ultraviolet

     (C) X-rays

     (D) Sound waves

107. Bluetooth is an example of: [BSEB, 2025]

     (A) PAN

     (B) LAN

     (C) WAN

     (D) MAN

108. In communication, ‘Decoding’ means: [BSEB, 2024]

     (A) Converting signal to information

     (B) Converting information to signal

     (C) Destroying signal

     (D) Amplification

109. Diameter of optical fibre core is approx: [BSEB, 2018]

     (A) 10-100 micrometers

     (B) 1-10 mm

     (C) 1 meter

     (D) 10 cm

110. Mass Spectrometer is used for: [BSEB, 2014]

     (A) Separation of isotopes

     (B) Catching radio waves

     (C) Image transmission

     (D) None of these

111. Digital communication is more reliable because: [BSEB, 2016]

     (A) Effect of Noise is less

     (B) It is fast

     (C) It is cheap

     (D) None of these

112. When TV tower height increases, the range of transmission: [BSEB, 2019]

     (A) Increases

     (B) Decreases

     (C) Remains same

     (D) Zero

113. Channel in a communication system can be: [BSEB, 2021]

     (A) Free space

     (B) Co-axial cable

     (C) Optical fibre

     (D) All of these

114. Efficiency of full-wave rectifier is: [BSEB, 2020]

     (A) 81.2%

     (B) 40.6%

     (C) 100%

     (D) 50%

115. Efficiency of half-wave rectifier is: [BSEB, 2020]

     (A) 40.6%

     (B) 81.2%

     (C) 50%

     (D) 25%

116. Minimum length of antenna should be: [BSEB, 2013]

     (A) $\lambda / 4$

     (B) $\lambda / 2$

     (C) $\lambda$

     (D) $2\lambda$

117. An $n-p-n$ transistor is: [BSEB, 2022]

     (A) Neutral

     (B) Negatively charged

     (C) Positively charged

     (D) None of these

118. Formula for TV signal distance $d$ is: [BSEB, 2023]

     (A) $d = \sqrt{2Rh}$

     (B) $d = 2Rh$

     (C) $d = \sqrt{Rh}$

     (D) $d = Rh$

119. IC (Integrated Circuit) was invented by: [BSEB, 2011]

     (A) Jack Kilby

     (B) Newton

     (C) Marconi

     (D) Ampere

120. Full form of LASER: [BSEB, 2017]

     (A) Light Amplification by Stimulated Emission of Radiation

     (B) Low Amplification Signal

     (C) Light And Sound

     (D) None of these

121. Waves used in mobile communication: [BSEB, 2025]

     (A) Radio / Microwaves

     (B) Infrared

     (C) Sound

     (D) Mechanical

122. Transistor can be used as: [BSEB, 2014]

     (A) Switch

     (B) Amplifier

     (C) Both (A) and (B)

     (D) Rectifier

123. An Antenna is a device for: [BSEB, 2020]

     (A) Receiving EM waves

     (B) Transmitting EM waves

     (C) Both (A) and (B)

     (D) None of these

124. FTP is a protocol for: [BSEB, 2026]

     (A) Sending files on internet

     (B) Sending mail

     (C) Browsing

     (D) Calling

125. The width of $p-n$ junction decreases in: [BSEB, 2023]

     (A) Forward bias

     (B) Reverse bias

     (C) Low doping

     (D) None of these

126. Top layer of a solar cell is made of: [BSEB, 2022]

     (A) $p$-type semiconductor

     (B) $n$-type semiconductor

     (C) Conductor

     (D) Insulator

127. For total internal reflection, angle of incidence should be: [BSEB, 2024]

     (A) Greater than critical angle

     (B) Less than critical angle

     (C) $90^\circ$

     (D) $0^\circ$

128. In $n$-type semiconductors, electrons are majority carriers, yet it is neutral because:

     (A) Atoms are neutral

     (B) Electrons and protons count is equal

     (C) Both (A) and (B)

     (D) None of these

129. The bandwidth of a signal is the:

     (A) Range of frequencies

     (B) Length of wire

     (C) Speed of signal

     (D) Power of signal

130. A geosynchronous satellite has an orbit height of approx:

     (A) 36000 km

     (B) 1000 km

     (C) 20000 km

     (D) 500 km