Q.1 Which of the following is the charge carrier in a p-type semiconductor?
Electrons
Holes
Neutrons
Protons
Explanation - In a p-type semiconductor, holes act as the majority charge carriers while electrons are the minority carriers.
Correct answer is: Holes
Q.2 The process of adding impurities to a pure semiconductor to increase its conductivity is called:
Diffusion
Doping
Polarization
Magnetization
Explanation - Doping introduces extra electrons (n-type) or holes (p-type) into the semiconductor, improving conductivity.
Correct answer is: Doping
Q.3 A diode allows current to flow:
In both directions
Only in reverse bias
Only in forward bias
Never
Explanation - Diodes are unidirectional devices that conduct in forward bias and block current in reverse bias.
Correct answer is: Only in forward bias
Q.4 The forbidden energy gap in a conductor is:
Very large
Zero
Finite but small
Infinite
Explanation - In conductors, the valence and conduction bands overlap, so the energy gap is zero.
Correct answer is: Zero
Q.5 Which material is commonly used in making solar cells?
Germanium
Silicon
Copper
Aluminum
Explanation - Silicon is the most widely used semiconductor material in solar cells due to its abundance and efficiency.
Correct answer is: Silicon
Q.6 In a transistor, the base is:
Thick and lightly doped
Thin and lightly doped
Thick and heavily doped
Thin and heavily doped
Explanation - The base is very thin and lightly doped to allow most charge carriers to diffuse through to the collector.
Correct answer is: Thin and lightly doped
Q.7 The unit of gain in communication systems is:
Bel
Decibel
Hertz
Watt
Explanation - Gain is expressed in decibels (dB), which is a logarithmic unit derived from Bel.
Correct answer is: Decibel
Q.8 Which of the following is used for rectification?
Zener diode
PN junction diode
Photodiode
Tunnel diode
Explanation - PN junction diodes convert AC into DC by allowing current only in forward bias, making them suitable for rectification.
Correct answer is: PN junction diode
Q.9 The maximum efficiency of a half-wave rectifier is approximately:
25%
40.6%
50%
81.2%
Explanation - A half-wave rectifier has a theoretical maximum efficiency of 40.6%.
Correct answer is: 40.6%
Q.10 In amplitude modulation (AM), which parameter of the carrier wave is varied?
Amplitude
Frequency
Phase
Velocity
Explanation - In AM, the amplitude of the carrier signal changes in accordance with the modulating signal.
Correct answer is: Amplitude
Q.11 The common emitter transistor configuration provides:
High input resistance, high output resistance
Low input resistance, high output resistance
High input resistance, low output resistance
Low input resistance, low output resistance
Explanation - The CE configuration is widely used as an amplifier because it provides high gain with low input resistance and high output resistance.
Correct answer is: Low input resistance, high output resistance
Q.12 Which of the following waves is not used for long-distance communication?
Sky wave
Space wave
Ground wave
Surface wave
Explanation - Surface waves are only useful for short distances due to high attenuation at longer distances.
Correct answer is: Surface wave
Q.13 Bandwidth of an amplitude-modulated signal is:
Equal to carrier frequency
Twice the modulating frequency
Equal to modulating frequency
Half the carrier frequency
Explanation - In AM, the bandwidth equals twice the highest frequency of the modulating signal.
Correct answer is: Twice the modulating frequency
Q.14 In communication systems, the range is directly proportional to:
Square of transmitted power
Square root of transmitted power
Inverse of transmitted power
Cube of transmitted power
Explanation - The maximum range of communication increases with the square root of the transmitted power.
Correct answer is: Square root of transmitted power
Q.15 A Zener diode is primarily used for:
Rectification
Voltage regulation
Amplification
Oscillation
Explanation - Zener diodes maintain a nearly constant voltage in reverse bias and are widely used in voltage regulation circuits.
Correct answer is: Voltage regulation
Q.16 The forward biasing of a diode decreases:
Depletion region width
Barrier potential
Resistance
All of the above
Explanation - Forward bias reduces the depletion width, lowers barrier potential, and decreases diode resistance.
Correct answer is: All of the above
Q.17 The energy gap of silicon at room temperature is approximately:
1.1 eV
0.7 eV
2.0 eV
5.0 eV
Explanation - The band gap of silicon is about 1.1 eV at room temperature, making it suitable for semiconductors.
Correct answer is: 1.1 eV
Q.18 Which type of modulation is most resistant to noise?
Amplitude modulation
Frequency modulation
Phase modulation
Pulse modulation
Explanation - FM is less affected by amplitude variations caused by noise, making it superior in noisy environments.
Correct answer is: Frequency modulation
Q.19 In a full-wave rectifier, the ripple frequency is:
Equal to input frequency
Twice the input frequency
Half the input frequency
Four times the input frequency
Explanation - The output of a full-wave rectifier has a ripple frequency that is double the input AC frequency.
Correct answer is: Twice the input frequency
Q.20 Which of the following devices works on the principle of photoelectric effect?
Zener diode
Photodiode
LED
Tunnel diode
Explanation - Photodiodes generate current when exposed to light due to the photoelectric effect.
Correct answer is: Photodiode
Q.21 In satellite communication, signals are transmitted using:
Ground waves
Sky waves
Microwaves
Surface waves
Explanation - Microwaves are used in satellite communication because they can penetrate the ionosphere with minimal attenuation.
Correct answer is: Microwaves
Q.22 Which transistor configuration provides unity voltage gain?
Common emitter
Common base
Common collector
None of these
Explanation - The common collector (emitter follower) has a voltage gain of nearly unity but provides high current gain.
Correct answer is: Common collector
Q.23 The most suitable semiconductor material for infrared LEDs is:
Silicon
Germanium
Gallium arsenide
Copper
Explanation - Gallium arsenide has a direct band gap suitable for emitting infrared radiation.
Correct answer is: Gallium arsenide
Q.24 In frequency modulation, the parameter varied is:
Amplitude
Frequency
Phase
Wavelength
Explanation - In FM, the frequency of the carrier signal is varied in proportion to the modulating signal.
Correct answer is: Frequency
Q.25 The cutoff frequency of an AM transmission is determined by:
Carrier frequency
Baseband signal
Bandwidth
Transmitter power
Explanation - The cutoff frequency depends on the highest frequency of the modulating signal, which defines the bandwidth.
Correct answer is: Bandwidth