# Capacitor Questions

Q9. A sinusoidal alternating voltage supply is connected to a bridge rectifier consisting of four ideal diodes. The output of the rectifier is connected to a resistor R and a capacitor C as shown in the diagram.

The function of C is to provide some smoothing to the potential difference across R. The variation with time t of the potential difference V across the resistor R is shown in the graph below.

(a) Use the graph to determine, for the alternating supply,

(i) the peak voltage

(1 mark)

(ii) the root-mean-square (r.m.s.) voltage

(1 mark)

(iii) the frequency

(2 marks)

(b) The capacitor C has capacitance 5.0 μF. For a single discharge of the capacitor through the resistor R, use the graph to

(i) determine the change in potential difference

(1 mark)

(ii) determine the change in charge on each plate of the capacitor,

(2 marks)

(iii) show that the average current in the resistor is 1.1 × 10–3 A.

(2 marks)

(c) Use the graph and the value of the current given in (b)(iii) to estimate the resistance of resistor R.

(2 marks)

(Total 11 marks)