What happens to the gain of a non-inverting amplifier using OP-AMP if the feedback resistor value is increased by 5 % while keeping the input resistor constant? (Assuming the OP-AMP remains in linear range for operation.)
The gain increases
To understand what happens to the gain of a non-inverting amplifier using an OP-AMP when the feedback resistor value is increased, we need to look at the gain formula for such a configuration.
The gain \( A_v \) of a non-inverting amplifier is given by the formula:
\(A_v = 1 + \frac{R_f}{R_{\text{in}}}\)
where:
- \(R_f\) is the feedback resistor connected between the output and the inverting input.
- \(R_{\text{in}}\) is the resistor connected between the inverting input and the ground.
If the feedback resistor \( R_f \) is increased by 5% while keeping the input resistor \( R_{\text{in}} \) constant, let's see how the gain changes:
- Initial value of feedback resistor: \(R_f\)
- Increased value of feedback resistor: \(R_f' = R_f + 0.05 R_f = 1.05 R_f\)
Substituting the new feedback resistor value into the gain equation gives:
\(A_v' = 1 + \frac{1.05 R_f}{R_{\text{in}}} = 1 + \frac{R_f}{R_{\text{in}}} + \frac{0.05 R_f}{R_{\text{in}}}\)
The expression \(\frac{0.05 R_f}{R_{\text{in}}}\) shows that the gain \(A_v'\) is greater than the original gain \(A_v\).
Therefore, when the feedback resistor is increased by 5%, the overall gain of the non-inverting amplifier increases.
Thus, the correct answer is: The gain increases.
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