Bipolar Junction Transistor (BJT) Basics and Characteristics Quiz Quiz

Challenge your understanding of bipolar junction transistor basics, operating regions, and electrical properties with this quiz designed for learners of electronics. Deepen your grasp of BJT characteristics, behavior in circuits, and related terminology for foundational semiconductor device knowledge.

1. BJT Terminal Identification

   Which terminals are found on a standard bipolar junction transistor (BJT) in the correct configuration?

   1. Source, Gate, Drain
   2. Input, Output, Ground
   3. Anode, Cathode, Grid
   4. Emitter, Base, Collector

   Explanation: A BJT has three terminals known as the emitter, base, and collector, which are essential for its function and current flow. 'Source, Gate, Drain' refer to field-effect transistors (FETs) and not BJTs. 'Anode, Cathode, Grid' are terminals of vacuum tubes or some diodes, and 'Input, Output, Ground' are general terms, not specific to any device. The specific terminal names are fundamental to understanding BJT operation.

2. BJT Operating Regions

   When a BJT is used as a switch and is in saturation, what is the biasing condition of its base-emitter and base-collector junctions?

   1. Both junctions are reverse-biased
   2. Both junctions are forward-biased
   3. Base-emitter is reverse, base-collector is forward-biased
   4. Base-emitter is forward, base-collector is reverse-biased

   Explanation: In saturation, both the base-emitter and base-collector junctions of a BJT are forward-biased, allowing significant current to flow from collector to emitter. If both junctions were reverse-biased, no conduction would occur. The base-emitter is forward and base-collector is reverse-biased in the active region, not saturation. The reverse-forward option does not occur in typical BJT operation modes.

3. Active Region Application

   In which region does a BJT operate when it functions as a linear amplifier, such as in audio applications?

   1. Cutoff region
   2. Breakdown region
   3. Active region
   4. Saturation region

   Explanation: A BJT acts as a linear amplifier in the active region, where the base-emitter junction is forward-biased and the base-collector junction is reverse-biased, allowing controlled amplification. The cutoff region means the BJT is fully off, and there is little to no collector current. Saturation is used for switching, not linear amplification, and the breakdown region can damage the device and is not a functional operating state.

4. Current Gain in BJTs

   Which parameter symbol refers to the DC current gain of a common-emitter BJT configuration?

   1. Eta (η)
   2. Gamma (γ)
   3. Alpha (α)
   4. Beta (β)

   Explanation: The current gain in a common-emitter BJT is symbolized by beta (β), representing the ratio of collector current to base current. Alpha (α) is the common-base current gain, which is always less than one. Gamma (γ) and Eta (η) are not standard symbols for current gain in BJT terminology, so these distractors are unrelated or incorrect.

5. BJT Symbol Identification

   How can you visually distinguish between NPN and PNP BJT symbols in circuit diagrams?

   1. Shape of the collector terminal
   2. Direction of the arrow on the emitter
   3. Color of the transistor symbol
   4. Presence of an additional lead

   Explanation: The arrow on the emitter indicates the type of BJT: NPN transistors have the arrow pointing out, while PNP transistors have it pointing in. The color of the transistor symbol is not defined in standard schematic diagrams. The shape of the collector terminal does not differ between symbols, and both types have just three leads, so no extra lead is present. This makes the arrow direction the key visual distinction.