 Solution

ID: past-exam-of-the-physics-2-paper-of-the-university-of-oxford/2013/8/ii/solution

The input source supplies

I_{i} = V_{i} / R_{i}

into the virtual ground, so the complete circuit's input resistance is

R_{i}

. The ideal output is a zero-resistance controlled voltage source:

R_{in} = R_{i}, R_{out} = 0.

These are properties of the closed-loop circuit, distinct from the infinite input resistance of the amplifier terminals themselves.

 New to topics? Read the docs here!