If R1=∞ and Rf =0 in the non inverting amplifier configuration. The amplifier act as a unity-gain amplifier or voltage follower.
The circuit consists of an op -amp and a wire connecting the output voltage to the input, i.e. the output voltagev is equal to the input voltage, both in magnitude and phase. V0=Vi.Since the output voltage of the circuit follows the input voltage, the circuit is called voltage follower. It offers very high input impedance of the order of MΩ and very low output impedance.
Therefore, this circuit draws negligible current from the source. Thus, the voltage follower can be used as a buffer between a high impedance source and a low impedance load for impedance matching applications.