For the circuit with an ideal OPAMP shown in the figure. $V_{\text {REF }}$ is fixed.

If $V_{\text {OUT }}=1$ volt for $V_{\text {IN }}=0.1$ volt and $V_{\text {OUT }}=6$ volt, for $V_{\text {IN }}=1 \mathrm{~V}$, where $V_{\text {OUT }}$ is measured across $R_{\mathrm{L}}$ connected at the output of this OPAMP. The value of $R_{\mathrm{F}} / R_{\text {IN }}$ is

Consider the circuit with an ideal OPAMP shown in the figure.

Assuming $\left|V_{\mathrm{IN}}\right| \ll\left|V_{\mathrm{CC}}\right|$ and $\left|V_{\mathrm{REF}}\right| \ll\left|V_{\mathrm{CC}}\right|$. The condition at which $V_{\text {OUT }}$ equals to zero is

A circuit with an ideal OPAMP is shown in the figure. A plus $V_{\text {IN }}$ of 20 ms duration is applied to the input. The capacitors are initially uncharged.

The components in the circuit shown below are ideal. If the op-amp is in positive feedback and the input voltage $V_i$ is a sine wave of amplitude 1 V , the output voltage $V_0$ is