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?

• A. $+ve$ terminal $1$, $-ve$ terminal $2$, resistance high
• B. $+ve$ terminal $2$, $-ve$ terminal $3$, resistance low
• C. $+ve$ terminal $3$, $-ve$ terminal $2$, resistance high
• D. $+ve$ terminal $2$, -$ve$ terminal $1$, resistance high

Answer 1

The correct option is D $+ve$ terminal $2$, -$ve$ terminal $1$, resistance high

For a pnp transistor, emitter and collector junction is taken from p terminal and base is taken from n terminal.

Multimeter can detect a short circuit (low resistance) and an open circuit (high resistance).

Low resistance is detected when positive of multimeter is connected at p-junction (1 or 3) and negative of multimeter is connected at n-terminal (2). Similarly, high resistance is detected when positive of multimeter is connected at n-junction (2) and negative of multimeter is connected at p-terminal (1 or 3).

Hence, d is the correct option.