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Q2. A 56 μF capacitor and a 68 kΩ resistor are connected in series to a 15 V d.c. power supply.

(a) Calculate EACH of the following:

(i) the instantaneous current when the supply is switched on; (2)

(ii) the capacitor voltage 3 seconds after switch-on; (3)

(iii) the energy stored in the capacitor 3 seconds after switch-on. (2)

(b) After 3 seconds of charging the supply is switched off and the capacitor is discharged through a 39 kΩ resistor.

(i) Calculate the time taken for the capacitor voltage to fall to 6 v. (3)

(ii) Using approximately scaled axes, sketch graphs of capacitor voltage against time for charge and discharge indicating:

• the supply voltage and the voltage 3 seconds after switch-on

• initial discharge voltage and the time when the voltage is 6 V (6)