The non-inverting amplifier shown in the following circuit uses a 741 Op-Amp with
R1=1K,R2=39K,R3=1K. The typical parameter values for the 741 Op-Amp are: Open loop
gain \$A_v = 2 × 10^5\$, Input resistance Ri=2M and Output resistance Ro=75ohm . What will be the Input resistance
and Output resistance for the non-inverting amplifier?
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You might be intrested in this question: https://electronics.stackexchange.com/questions/304521 – PlasmaHH Jun 19 '17 at 13:26
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Do you know about the effects of negative feedback? – LvW Jun 19 '17 at 13:43
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For output resistance to be controlled, the circuit needs 1/GH to be greater than 1. A unity gain follower, with H=1 (not your circuit), has 1/GH > 1 for all frequencies up to UGBW which for the UA741 is 0.5 or 1.0MHz.
In your circuit, the H is (R2 + R3) / R3 = 40K/1k = 40. This means, your opamp has no control over output resistance for frequencies higher than $$UGBW * (1/40)$$ or 1.0MHz / 40 == 25KHz.
For your circuit, above 25KHz, the Rout will be 75 ohms. Approximately.
Notice the 1/G*H controls behavior. That factor results from math analyzing the negative feedback. Write out that math
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