NEET Physics Semiconductor Electronics Questions Solved

NEET - 2008

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

(a) 90                            (b) 10

(c) 1.25                         (d) 100

The process of injection a fraction of output energy of some device back to the input is known as feedback. When the feedback energy(voltage or current) is out of phase with input signal and thus opposes it, it is called negative feedback.

Voltage gain with feedback is 

         Avf=Av1+βAv

where Av is voltage gain without feedback and β is negative feedback.

Given Avf=10, β=9%=9100

              10=Av1+9100Av

 

or        10+910Av=Av

or        0.1 Av=10 or Av=100

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