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Inverting amplifier (op-amp)

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Objective

Build a −10 amplifier with an op-amp and verify Vout = −(Rf/Ri)·Vin.

Procedure

Run and read the output voltage.
Change Rf to 20 kΩ: the gain doubles.
Raise Vin to 2 V: the output saturates near −13 V.

Theory

The virtual short keeps the inverting input at 0 V, so Iin = Vin/Ri flows through Rf: Vout = −(Rf/Ri)·Vin = −10 × 0.5 V = −5 V. Input resistance equals Ri.

Questions to answer

Why is the inverting input called a virtual ground?

Components used

3 × Battery / DC source, Op-Amp LM741, 2 × Resistor 220 ohm 1/4W

About the model

Ideal wires; component models as listed in the catalogue (no parasitics, no temperature drift). Built without a breadboard so the schematic stays readable.