(i) When an AC source is connected to an ideal inductor show that the average power supplied by the source over a complete cycle is zero.
(ii) A lamp is connected in series with an inductor and an AC source. What happens to the brightness of the lamp when the key is plugged in and an iron rod is inserted inside the inductor ? Explain.
Average power supplied by the source over a complete cycle is,
P = VI cos 
;
cos 
is called as the power factor.
For a pure inductive circuit,
Phase difference between current and voltage = 
And, cos 
Therefore,
Average power dissipated = 0
ii) The brightness of the lamp decreases because when an iron rod is inserted in the inductor, the value of inductance L increases. Therefore, the current flowing across the bulb will decrease, thus decreasing the brightness of the bulb.
