Question

A common emitter transistor amplifier has a collector current of 10mA, when its base current is 25µA at the room, temperature. What is input resistance?

(a) 3kΩ

(b) 5kΩ

(c) 1kΩ

(d) 7kΩ

This question was posed to me in unit test.

My question comes from Biasing Parameters topic in division Small-Signal Low-Frequency AC models of Transistors of Electronic Devices & Circuits

Answer 1

Correct choice is (c) 1kΩ

To explain I would say: We know, β/gm=ri

= (IC/IB)/(IC/VT)=VT/IB=25m/25µ=1k.