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Dr. Carlotta A. Berry, PhD

I have a non-inverting amplifer with a 1 kohm input resistor. If it needs to have a gain of 2.5, what is the value of the feedback resistor.

The answer is 1.5 kohms because the formula is gain is
1 + R2/R1 where R2 is the feedback resistor and R1 is the input resistor.

@drcaberry 🤔 Being a non-inverting amplifier .... if there is ALSO a 1K resistor between the inverting input and reference AND we are talking about a differential op-amp, then the answer is 1K5. The input resistor of the non-inverting input will not effect the gain but may effect the offset voltage (due to non-zero input current).

@vk2bea The input resistor is the one tied to grounds from the inverting input. There could also be one a the voltage soure to the non-inverting input but it won't impact the gain. This is not a difference amplifier, I'm trying to keep things simple. 👍🏾

@drcaberry

What IS the answer!? I must know!

Also work on yer book. :apartyblobcat:

@albinanigans Thank you! The answer is 1.5 khoms because the formula is gain is 1 + R2/R1 = 1+1.5/1 = 2.5