Electronics quiz

Transistors quiz

BJTs as switches and amplifiers - base, collector, emitter and what turns them on.

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18 questions in the app. A few of them, with their answers:

1. What are the three terminals of a bipolar junction transistor (BJT)?

   • Anode, cathode, gate
   • Base, collector, emitter ✓
   • Source, drain, gate
   • Positive, negative, ground

   Answer A BJT has three terminals: base, collector and emitter.

2. In an NPN transistor used as a switch, a small current into which terminal turns it ON?

   • Collector
   • Emitter
   • Base ✓
   • Ground

   Answer A small base current controls a much larger collector current - that amplification is what makes it useful as a switch.

3. What does a transistor's current gain (β, or hFE) describe?

   • The ratio of collector current to base current ✓
   • The voltage drop across the base-emitter junction
   • The maximum voltage it can block
   • The transistor's physical size

   Answer β = Ic / Ib - how many times larger the collector current is than the base current driving it.

4. A transistor used as a simple switch (e.g. driving an LED) is normally operated in which two regions?

   • Only the active (linear) region
   • Cutoff (fully off) and saturation (fully on) ✓
   • Only reverse breakdown
   • The active region with negative feedback

   Answer A switch wants only two states: cutoff (no current) and saturation (as much current as the circuit allows) - not the in-between linear region.

5. What is "saturation" in a BJT switch?

   • The transistor is fully off, no current flows
   • The transistor is fully on, and Vce drops to a small residual voltage ✓
   • The transistor has overheated
   • The base current has reversed direction

   Answer In saturation the transistor is driven as hard on as it can go - collector current is set by the external circuit, and Vce sits at a small residual value (often under 0.3 V).

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