Non-Inverting Op-Amp Gain

Here the signal goes straight to the non-inverting input, and R_f with R_in form a divider that feeds a sample of the output back. Feedback forces that sample to equal the input, so the output must be larger by the divider's reciprocal: G = 1 + R_f/R_in. With 90 kΩ and 10 kΩ the gain is 10, in phase this time, and the input impedance is enormous — megohms to gigohms — because the signal only has to charge the op-amp's input capacitance.

That high input impedance is the reason this configuration dominates sensor front ends, where loading the source would corrupt the reading. The "one" cannot be removed: set R_f to zero and you get the unity-gain buffer, a follower with essentially infinite input and near-zero output impedance, which is the single most common op-amp circuit in existence. Attenuation, though, is impossible here — for gains below one, put a divider ahead of the buffer.