Figure 7.1 shows the circuit arrangement of an inverting amplifier using an ideal operational amplifier (op-amp).
(a(i))[3]
Explain why point P is described as a virtual earth.
(a(ii))[2]
Calculate the amplifier gain.
(b)[3]
The potential difference across the LED is $2.3\,\text{V}$ when the op-amp is saturated. Calculate the minimum value of resistor $R$ needed to restrict the LED current to $30\,\text{mA}$.
Worked solution & mark scheme
This 8-mark question has a full step-by-step worked solution and mark scheme. One marking point: “The amplifier gain is very large, or ideally infinite.” …