A circuit incorporating an ideal operational amplifier (op-amp) is shown in the figure below.
State the name of this circuit.
Explain why the point P is referred to as a virtual earth.
The circuit in the figure above is modified, as shown in the figure below.
The voltmeter has infinite resistance and its full-scale deflection is 
. The input potential to the circuit is 
. The switch position may be changed in order to have different values of resistance in the circuit. The input potential and the switch position are varied. For each switch position, the reading of the voltmeter is . Complete the table below for the switch positions shown.
and 
must be almost zero. Now, the non-inverting input is connected to the zero-volt line (earth), so 
, therefore, for the amplifier not to saturate, 
