An inverting feedback stage treats the virtual node as a current ledger, then turns that current into an output voltage through the feedback resistor. These rows make the negative output exact only for the declared current, resistor, and ideal op-amp assumptions; real stages have finite open-loop gain and bandwidth, input offset and bias current, resistor tolerance, rail headroom, slew limits, loading, noise, temperature drift, and voltage/current measurement uncertainty.
Holding input current fixed makes the inverting gain relationship visible across three rows. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Equal resistors give unit inverting gain
The input current is 1 ampere. With feedback resistance 2 ohms, the output is -2 volts.
Vout=−(1A)⋅2ohm=−2V
More feedback resistance makes more negative output
The input current stays 1 ampere, while feedback resistance rises to 4 ohms. The output becomes -4 volts.
Vout=−(1A)⋅4ohm=−4V
The same current gives a third output point
The final row keeps the input side fixed and uses 6 ohms in feedback. The output is -6 volts.