Electronic Devices and Circuits Questions and Answers – Class B Amplifiers

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This set of Electronic Devices and Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Class B Amplifiers”.

1. Where does the Q point lie for class B amplifier?
a) Active
b) Cut off
c) Saturation
d) Between saturation and active
View Answer

Answer: b
Explanation: Class B amplifier are designed by fixing the Q point in cut off region of the transfer characteristic.
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2. Class B amplifier Produces output even if the input is zero.
a) True
b) False
View Answer

Answer: b
Explanation: When input provided to the class B amplifier is zero, no output will be achieved, because it is excellent against noise.

3. What happens when class B amplifier is in a quiescent state?
a) No current flows through the transistor
b) Maximum current flows through the transistor
c) Half of the maximum current flows through the transistor
d) Quarter of the maximum current flows
View Answer

Answer: a
Explanation: When the transistor is in a quiescent state, no input is applied across the base terminal of the transistor and hence no current flows through the transistor.

4. What is the value of the maximum efficiency of the class B amplifier?
a) 25%
b) 35%
c) 35% to 50%
d) 50% to 70%
View Answer

Answer: d
Explanation: Class B amplifiers are more efficient compare to the class A amplifier because of good protection against noise effects.

5. Which is the main disadvantage of class B amplifiers?
a) Expensive
b) Less efficient
c) More power dissipation
d) More heat dissipation
View Answer

Answer: a
Explanation: Since class B amplifier uses a balanced centre-tapped transformer in its design, making it expensive to construct.
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6. What kind of design is used to avoid transformer usage?
a) High resistance
b) Matched load
c) Complementary symmetry
d) Capacitive Model
View Answer

Answer: c
Explanation: To avoid transformer usage in Class B amplifier, pair of transistor is connected together in complemented manner.

7. What is cross over distortion?
a) Effect occurred during switching of transistor after every half cycle
b) Distortion occurred due to resistors
c) Distortion occurred due to Capacitors
d) Distortion occurred due to Inductors
View Answer

Answer: a
Explanation: Transistor takes 0.7V to turn on when during the end of half cycles, the input gets below 0.7V and it is not possible to reproduce these signals. This is called as Cross over distortion.

8. How to avoid cross over distortion?
a) By using more resistance
b) By using more capacitance
c) By using more Inductance
d) By shifting the Q point above cut off
View Answer

Answer: d
Explanation: By using two more voltage sources and thus by shifting the Q point slightly above the cut off, we can remove noise over distortion.

9. For a Class B amplifier, the utilized load power is 300W and the Dc power is 500W, find efficiency.
a) 30%
b) 60%
c) 90%
d) 100%
View Answer

Answer: b
Explanation: Efficiency=ac power/dc power
Efficiency=300/500 = 3/5 = 0.6.
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10. What is the conduction angle for Class B push-pull amplifier?
a) 0
b) 90
c) 180
d) 270
View Answer

Answer: c
Explanation: For class B push-pull amplifier, the conduction angle is 180 degree that is it amplifies only one half cycle of the input in one time period.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn