AC circuit containing only a capacitor:
Consider a circuit containing a capacitor of capacitance C connected across an alternating voltage source.
The alternating voltage is given by
Vm sin ωt …… (1)
Let q be the instantaneous charge on the capacitor. The emf across the capacitor at that instant \(\frac{q}{C}\) is . According to Kirchoff’s loop rule,.
υ = \(\frac{q}{C}\) = 0
⇒ CVm sin ωt
By the definition of current,
where \(\frac{\frac{V_m}{1}}{\frac{1}{Cω}}\) = Im,
The peak value of the alternating current. From equation (1) and (2), it is clear that current leads the applied voltage by π/2 in a capacitive circuit. The wave diagram for a capacitive circuit also shows that the current leads the applied voltage by 90°.
