Question:
An unknown transistor needs to be identified as a \(npn\) or \(pnp\) type. A multimeter, with +ve and -ve terminals, is used to measure resistance between different terminals of transistor. If terminal 2 is the base of the transistor then which of the following is correct for a \(pnp\) transistor ?
An unknown transistor needs to be identified as a \(npn\) or \(pnp\) type. A multimeter, with +ve and -ve terminals, is used to measure resistance between different terminals of transistor. If terminal 2 is the base of the transistor then which of the following is correct for a \(pnp\) transistor ?
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In a pnp transistor the base is n-type: +ve on the base and -ve on emitter/collector reverse-biases the junction (high resistance); +ve on emitter/collector and -ve on base forward-biases it (low resistance).
Updated On: Nov 11, 2026
- +ve terminal 1, -ve terminal 2, resistance high
- +ve terminal 2, -ve terminal 1, resistance high
- +ve terminal 3, -ve terminal 2, resistance high
- +ve terminal 2, -ve terminal 3, resistance low
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The Correct Option is B
Solution and Explanation
For a \(pnp\) transistor the emitter and collector are p-type and the base (terminal 2) is n-type.
Take +ve of the meter as the positive (higher potential) terminal. If +ve is on a p-region (1 or 3) and -ve on the base, the junction is forward biased, so the resistance is low. Options (1) and (3) say 'high' for this connection, which is the behaviour of an \(npn\) transistor, so they are wrong.
If +ve is on the base (n-type) and -ve on terminal 1 (p-type), the junction is reverse biased, so the resistance is high. Option (2) states exactly this.
Option (4) has +ve on the base and -ve on terminal 3, which is also reverse bias, so the resistance would be high, not low.
Answer: (2) +ve terminal 2, -ve terminal 1, resistance high
Take +ve of the meter as the positive (higher potential) terminal. If +ve is on a p-region (1 or 3) and -ve on the base, the junction is forward biased, so the resistance is low. Options (1) and (3) say 'high' for this connection, which is the behaviour of an \(npn\) transistor, so they are wrong.
If +ve is on the base (n-type) and -ve on terminal 1 (p-type), the junction is reverse biased, so the resistance is high. Option (2) states exactly this.
Option (4) has +ve on the base and -ve on terminal 3, which is also reverse bias, so the resistance would be high, not low.
Answer: (2) +ve terminal 2, -ve terminal 1, resistance high
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