An electric iron consumes energy at a rate of 840 W when heating is at the maximum rate and 360 W when the heating is at the minimum. The voltage is 220 V. What are the current and the resistance in each case?

Explanation

From Eq. (12.19), we know that the power input is
P = V I
Thus the current I = P/V
(a) When heating is at the maximum rate,
I = 840 W/220 V = 3.82 A,
and the resistance of the electric iron is
R = V/I = 220 V/3.82 A = 57.60 `Omega `
(b) When heating is at the minimum rate,
I = 360 W/220 V = 1.64 A,
and the resistance of the electric iron is
R = V/I = 220 V/1.64 A = 134.15 `Omega `