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Capacitor Questions

** Q6.** A capacitor, initially charged to a pd of 6.0V, was discharged through a 100 kΩ resistor.

A datalogger was used to record the pd across the capacitor at frequent intervals. The graph shows how the pd varied with time during the first 40 s of discharge.

(a)

(i) Calculate the initial discharge current.

**(1 mark)**

(ii) Use the graph to determine the time constant of the circuit, giving an appropriate unit.

**(4 marks)**

(iii) Hence calculate the capacitance of the capacitor in microfarads.

**(1 mark)**

(iv) Show that the capacitor lost 90% of the energy it stored originally after about 25 s.

**(3 marks)**

(b) In order to produce a time delay, an intruder alarm contains a capacitor identical to the capacitor used in the experiment in part (a). This capacitor is charged from a 12V supply and then discharges through a 100 kΩ resistor, similar to the one used in the experiment.

(i) State and explain the effect of this higher initial pd on the energy stored by this capacitor initially.

**(2 marks)**

(ii) State and explain the effect of this higher initial pd on the time taken for this capacitor to lose 90% of its original energy.

**(1 mark)**

**(Total 12 marks)**