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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.
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Solution
Given: V = 220 V
Pmin = 360 W
Pmax = 840 W
When the heating is minimum,
Pmin = 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,
Pmax = VI
⇒ 840 = 220 I
⇒ I = `840/220`
⇒ I = 3.81 amp
R = `V/I`
⇒ R = `220/3.81`
⇒ R = 57.74 ohms
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