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

In the case of minimum heating:

P = 360 W
V = 220 V
where the symbols used have their usual meanings.
We know that  P = VI 

`I=p/V` 

`I=360/220=1.64 A` 

Resistance,`R V/I` 

`R=220/1.64=134.15`Ω 

In the case of maximum heating: 

P = 840 W
V = 220 V
where the symbols used have their usual meanings.
We know that P = VI 

`I=P/V` 

`I=840/220=3.82A` 

further,`R=V/I` 

`R=220/3.82=57.60`Ω