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
1. What is the main doping structure of a Bipolar Junction Transistor (BJT)?
- Three alternating p and n layers (p-n-p or n-p-n)
- A single uniform p-type slab
- A MOS capacitor structure
- A Schottky barrier diode structure
2. In an NPN transistor, which region is the majority charge carrier emitter?
- Holes in p-type material
- Electrons in n-type material
- Ions in intrinsic region
- Majority holes in n-type
3. Which terminal of a BJT controls the base current to modulate collector current?
- Emitter
- Collector
- Base
- Substrate
4. What is the typical relationship between collector current (IC) and base current (IB) in active region?
- IC is proportional to IB via β
- IC equals IB squared
- IC is independent of IB
- IC is inverse of IB
5. Which region must the base-emitter junction be biased to operate a BJT in active mode?
- Base-emitter forward biased and base-collector reverse biased
- Both junctions reverse biased
- Both junctions forward biased
- Base-emitter reverse biased and base-collector forward biased
6. What is meant by "saturation" in a BJT?
- Both base-emitter and base-collector are forward biased
- Both junctions reverse biased
- Base-emitter forward, base-collector reverse
- Emitter-collector shorted internally
7. What is "cut-off" condition of a BJT?
- Transistor fully on
- No current flows (transistor off)
- Only base current flows
- Collector-emitter short-circuit only
8. Which parameter represents the small-signal current gain of a BJT?
- h_fe (or β)
- gm
- r_o
- Cje
9. Which of these increases when the emitter doping is made heavier while keeping other regions same?
- Emitter injection efficiency increases
- Base resistance increases
- Collector leakage increases
- Transistor becomes PNP
10. What is "early effect" in BJTs?
- Base width modulation by VCB (Early effect)
- Avalanche breakdown of base
- Thermal runaway effect
- Punch-through only