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On connecting a battery the device passes a current, but when the battery is reversed, the current drops to almost zero. The device may be

Asked in CBSE AIPMT 1998 · Biasing and I-V characteristics

Answer: (3) a p-n junction

Step-by-step solution

Idea: conducting one way and not the other means the device is not symmetric, so it cannot be a uniform piece of material.

A p-n junction has a built-in barrier that an applied voltage can either oppose or reinforce.

Forward bias lowers the barrier and lets current flow freely.

Reverse bias raises it, leaving only the tiny minority-carrier current, which is close enough to zero to be called none.

Why the other options are wrong

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