A-Level AQA Physics Current–Voltage Characteristics: Figure 1 shows a circuit contain

Question

Figure 1 shows a circuit containing an ideal operational amplifier. A signal $V_{in}$ is applied to one of the amplifier inputs.

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1.1 Draw an X on the circuit in Figure 1 to indicate a virtual earth point.

1.2 Show that the closed loop voltage gain for the amplifier in Figure 1 is given by:

$$A_{v} = -\frac{R_f}{R_{in}}$$

State any assumptions made in your answer.

1.3 Figure 2A shows the input signal $V_{in}$ that is applied to the circuit in Figure 1.

1.4 The circuit in Figure 1 has a closed loop gain of -20 and has power-supply voltages of ±6.0 V.

Draw, on Figure 2B, the output waveform from the operational amplifier circuit over the same time interval as that shown on Figure 2A.

1.4 A student converts the circuit in Figure 1 into one that will add two input signals $V_1$ and $V_2$.

The new circuit produces an output voltage $V_{out}$ so that:

$$V_{out} = - (1.5 	imes V_1 + 0.75 	imes V_2)$$

The circuit is to include a 27 kΩ feedback resistor.

Complete Figure 3 to show the circuit that the student constructs. Annotate your circuit with the values of any additional components.

Figure 1 shows a circuit containing an ideal operational amplifier - AQA - A-Level Physics - Question 1 - 2022 - Paper 8