Question

A n-p-n transistor is used in common emitter mode in an amplifier it. A change of 40μA in the base current changes the output current by 2mA and 0.04 V in input voltage. 

The input resistance is________. 

(A) 1kΩ 

(B) 10Ω 

(C) 10kΩ 

(D) 100Ω

Answer 1

The correct option is (A) 1kΩ.

Explanation:

Given is the common emitter mode

hence Δ V_in = Δ V_BE = 0.04 V

ΔI_B = 40μA

ΔI_C = 2 mA

we know r_input = {(ΔV_BE) / (ΔI_B)}

∴ r_input = {(0.04) / (40 × 10^–6)} = {(4 × 10^–2) / (4 × 10^–5)} = 10³ Ω

∴ r_input = 1kΩ