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A n-p-n transistor conducts when

Asked in CBSE AIPMT 2003 · Transistor structure and action

Answer: (2) collector is positive and emitter is negative with respect to the base

Step-by-step solution

Idea: active mode needs one junction driven forward and the other held back, so take the two junctions separately.

The base of an n-p-n device is p-type. To drive the emitter junction into conduction the base has to sit above the emitter in potential.

Read from the base, that means the emitter sits below it.

The other junction has to be held back instead, which puts the collector above the base.

Putting the two together: collector high, emitter low, both measured against the base.

Why the other options are wrong

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