If the feedback resistor is doubled from its original value while the input resistor remains the same and the initial gain is 75, what is the new gain?

If the feedback resistor is doubled from its original value while the input resistor remains the same and the initial gain is 75, what is the new gain?

• A. 75
• B. 37.5
• C. 150
• D. 225

Answer: (C)

In an inverting op-amp, the closed-loop gain magnitude is set by the ratio Rf/Rin. If the input resistor stays the same and the feedback resistor is doubled, that ratio doubles. Starting from a gain magnitude of 75, doubling Rf yields a magnitude of 150. If you track the sign for an inverting configuration, the gain would be -150, but the numerical gain value asked here is 150.

In an inverting op-amp, the closed-loop gain magnitude is set by the ratio Rf/Rin. If the input resistor stays the same and the feedback resistor is doubled, that ratio doubles. Starting from a gain magnitude of 75, doubling Rf yields a magnitude of 150. If you track the sign for an inverting configuration, the gain would be -150, but the numerical gain value asked here is 150.