An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be -

• (a) 100W
• (b) 75W
• (c)50W
• (d) 25W

(d)25W
Power of an appliance determines the rate at which electrical energy is delivered to it. Power of an appliance is given by the expression, P = VI = V2/R R =V2/P where, Power rating, P = 100 W Voltage, V = 220 V Resistance, R = 484 ohm The resistance of the bulb remains constant if the supply voltage is reduced to 110 V. If the bulb is operated on 110 V, then the energy consumed by it is given by the expression for power as