The voltage gain of an amplifier with `9%` negative feedback is `10`. The voltage gain without feedback will be

Options

A. 90
B. 10
C. 125
D. 100

Answer

D

Explanation

Voltage gain with feedback is, `A_(V_(f))=(A_(V))/(1+betaA_(V))`
where `A_(V)` is voltage gain without feedback and `beta` is negative feedback.
Given `A_(Vf)=10, beta=9%=(9)/(100)`
`therefore 10=(A_(V))/(1+(9)/(100)A_(V)) rArr 10+(9)/(10)A_(V)=A_(V)`
`or 0.1 A_(V)=10 or A_(V) = 100`