(a(i))[4]
Using the properties of an ideal op-amp, explain why point $P$ is called a virtual earth.
(a(ii))[4]
Derive an expression for the gain of the amplifier circuit in terms of the resistances $R_1$ and $R_2$.
(b)[3]
For the circuit in Fig. 7.1, the ratio $\frac{R_2}{R_1}$ is $4.5$. The change with time $t$ of the input potential $V_{IN}$ is shown in Fig. 7.2. On Fig. 7.2, show the change with time $t$ of the output potential $V_{OUT}$.