(iii) Sketch using the same axes the graphs of charge Q on the capacitor and current I in the circuit against time.

Sketch using the same axes the graphs of charge Q on the capacitor and current I in the circuit against time.

Explanation of the curve

• Charge C = CV, thus charge is greatest when voltage is greatest.
• This curve shows that the maximum voltage across the capacitor occurs π/2 radians after the maximum rate of change of voltage. At the exact moment when the voltage across the capacitor is greatest, the voltage is neither rising nor falling. Therefore, the instantaneous current must be zero at this instant.
• The maximum rate of change of voltage occurs when the voltage sine curve is steepest. At this instant the voltage is zero, indicating that the capacitor has just finished discharging its stored charge and is about to start building up an opposite charge. Therefore, the instantaneous current has its maximum positive value at the instant when the voltage across the capacitor changes from a negative polarity to a positive polarity

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