JEE Main 2022 · 27 June · evening · Single correct · +4 / −1
For a transistor to act as a switch, it must be operated in
- (a) Active region.
- (b) Saturation state only.
- (c) Cut-off state only.
- (d) Saturation and cut-off state.
Answer and solution
Answer (d) Saturation and cut-off state.
Solution
Physics sir · 3 steps
A switch needs exactly two states, OFF and ON, so the transistor must jump between cut-off and saturation.
- What a switch does. A switch has only two useful states: fully OFF (no current) and fully ON (maximum current, almost no voltage across it). The transistor must reproduce both.
Region Junction biasing Collector current Behaves like Cut-off both junctions reverse biased I_C ≈ 0 switch OFF Active emitter forward, collector reverse I_C = β I_B, varies smoothly amplifier Saturation both junctions forward biased maximum, V_(CE) ≈ 0 switch ON - Switching action. A low input voltage drives the transistor into cut-off and a high input drives it into saturation. It passes through the active region only briefly while changing state.
- So. Switching needs both the saturation state and the cut-off state, which is option (d).
The idea to keep. Amplifier means active region. Switch means cut-off for OFF and saturation for ON. One state alone can never make a switch.
Answer from the NTA final answer key. Solution by PrepWiser.