Question

An electric iron is connected to the mains power supply of 220 V. When the electric iron is adjusted at ‘minimum heating' it consumes a power of 360 W but at 'maximum heating’ it takes a power of 840 W. Calculate the current and resistance in each case.

Answer 1

Given: V = 220 V

P_min = 360 W

P_max = 840 W

When the heating is minimum,

P_min = VI

⇒ 360 = 220 I

⇒ I = `360/220`

⇒ I = 1.63 amp

R = `V/I`

⇒ R = `200/1.63`

⇒ R = 134.96 ohms

When the heating is maximum,

P_max = VI

⇒ 840 = 220 I

⇒ I = `840/220`

⇒ I = 3.81 amp

R = `V/I`

⇒ R = `220/3.81`

⇒ R = 57.74 ohms