Calculate the current drawn by an appliance rated 110 W, 220 V when connected across 220 V supply.
Topic: Current, resistance and circuits
Answer
Given: appliance rated 110 W, 220 V, connected across a 220 V supply.
Since the supply voltage equals the rated voltage, the appliance works at its rated power.
P = V I I = P ÷ V = 110 ÷ 220 = 0.5 A
Current drawn = 0.5 A
A rating of "110 W, 220 V" means the appliance consumes 110 W WHEN it is run at 220 V. Because the supply here is also 220 V, you can use the rated figures directly.
P = VI rearranged gives I = P/V. Dividing the other way, 220 ÷ 110, gives 2 A — the standard inverted answer. Sanity-check it: a 110 W appliance is a small one, about the draw of a bright bulb, so a fraction of an amp is the right size.
If the supply voltage had been different from the rating, you would first find the resistance from R = V²/P using the RATED values, then use the actual supply voltage with that resistance.