The voltage follower with an ideal op amp gives simply

but this turns out to be a very useful service, because the input impedance of the op amp is very high, giving effective isolation of the output from the signal source. You draw very little power from the signal source, avoiding "loading" effects. This circuit is a useful first stage.

The voltage follower is often used for the construction of buffers for logic circuits.

A circuit for converting small current signals (>0.01 microamps) to a more easily measured proportional voltage.

By the current rule:

so the output voltage is given by the expression above.

The current output through the load resistor is proportional to the input voltage

The behavior of most configurations of op-amps can be determined by applying the "golden rules".For the voltage-to-current amp the voltage rule tries to make the voltage at 3 equal to the input voltage , so

but to drop the output voltage to ground requires

and substituting gives