In a feedback amplifier for which the open loop gain $A_{O L} = 10^{4}$ and the closed loop gain after the negative feedback $A_{C L} = 10^{3}$ . Then the amount of feedback factor $^{'} β^{'}$ that is employeed in this scheme is ________ $\times 10^{- 6}$ .
900

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Solution

The correct option is A 900
$A_{C L} = \frac{A_{O L}}{1 + β A_{O L}}$

$10^{3} = \frac{10^{4}}{1 + 10^{4} β}$

$10^{3} + 10^{7} β = 10^{4}$

$β = \frac{10^{4} - 10^{3}}{10^{7}} = \frac{9 \times 10^{3}}{10^{7}} = 900 \times 10^{- 6}$

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An amplifier has open loop gain of A_{O L} = 5 \times 10^{3} . The amplifier is connected by the negative feedback with feedback factor β = 0.01 . If the open loop gain of op-amp decreases by 10% then the closed loop gain decreased by_____%.

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