Junction Transistors (BJT) Questions and Answers
The Junction Transistors (BJT) questions with answers topic is an integral part of electronics aptitude questions and answers for technical exams such as GATE, DRDO, and BEL. A Bipolar Junction Transistor (BJT) is a semiconductor device used for amplification and switching. Understanding its types (NPN, PNP), working principles, and characteristics is vital for solving objective and circuit-based questions. This section provides solved BJT questions with explanations to help you grasp current gain, transistor biasing, and operating regions effectively.
Junction Transistors (BJT)
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25 questions
11. Which configuration provides maximum input impedance for a BJT amplifier?
- Common-collector (emitter follower)
- Common-base
- Common-emitter
- Differential pair
12. In a common-emitter amplifier, a 180° phase shift appears between input and output because?
- Because collector and base currents are equal
- Because collector voltage is inverted relative to base input
- Because emitter is floating
- Because base-emitter junction conducts in reverse
13. What happens to collector current if base-emitter forward bias increases slightly (in active region)?
- Collector current decreases with VBE
- Collector current increases approximately exponentially with VBE
- Collector current is linear with VBE
- Collector current independent of VBE
14. Which parameter is reduced by adding emitter degeneration resistor in series with emitter?
- Voltage gain increases
- Gain is reduced and linearity improved
- Transistor becomes unstable
- Input impedance drastically decreases
15. Which junctions are present in a PNP transistor?
- p-type emitter, n-type base, p-type collector
- n-type emitter, p-type base, n-type collector
- All n-type regions
- Metal-semiconductor junction only
16. What is the approximate VBE (base-emitter voltage) for silicon BJTs in forward active region?
- Approximately 0.7 V
- Approximately 5 V
- Approximately 0.01 V
- Approximately 2 V
17. Which effect causes collector current to slightly depend on collector-base voltage even in active mode?
- Early effect (base-width modulation)
- Zener effect
- Hall effect
- Photoelectric effect
18. What is the usual role of the base region in a BJT?
- To be thin and lightly doped so carriers pass with minimal recombination
- To be heavily doped so it supplies carriers
- To act as a perfect insulator
- To supply majority holes only
19. Why is the emitter usually heavily doped compared to base?
- To increase injection efficiency and gain
- To reduce collector-emitter voltage
- To make base thicker
- To convert transistor to FET
20. Which BJT configuration has unity voltage gain approximately but high current gain?
- Common-collector has unity voltage gain and high current gain
- Common-base has unity current gain
- Common-emitter has unity voltage gain
- None of the above