Q.Calculate the input voltage when $V_o = 11\text{ V}$.

The non-inverting amplifier applies the input signal $V_1$ directly to the non-inverting $(+)$ terminal of the op-amp. The inverting $(-)$ terminal is connected to ground through a resistor $R_i$, and a feedback resistor $R_f$ returns part of the output to that same inverting node.

Because of negative feedback, the inverting input is forced to the same voltage as the non-inverting input, so the voltage at the inverting node equals $V_1$. This voltage appears across $R_i$, and since the ideal input draws no current, the same current flows through $R_f$. Working through the node equation gives the output voltage and gain:

Key features distinguish it from the inverting amplifier:

• The output is in phase with the input (no sign reversal).
• The gain is always greater than or equal to one, and again is set only by the resistor ratio. …