The element of a 500 watt electric iron is designed for use on a 200 volt supply. What value of resistance is needed to be connected in series in order that the iron can be operated from 240 volt supply?
Since the iron is rated for 500 W, 200 V, the resistance of the iron coil is,
When an external resistance Rx is connected in series with the iron, the total resistance in the circuit is RT = (R + Rx). If this is connected to a 240 V supply, the power equation becomes,