What is the input resistance of the transistor if a change of 200 mV in base-emitter voltage causes a change of 100μA in the base current?

2 kΩ 2 Ω 2 mΩ 100 kΩ

2 kΩ

ΔVbe​=200 mV=2×10−3V, ΔIb​=100μA=10−6 A,  For transistors, the input resistance is Ri​=​ΔVbe/ΔIb​​= 2×10−3/10−6​,   Ri​=2×103=2 KΩ