Question

A torch bulb is rated 6 V and 750 mA. Calculate the energy consumed by the bulb in 4 hours.

Answer 1

The potential difference of the bulb = 6 V
Amount of current passed through the bulb = 750 mA = 0.75 A
Power of the bulb = potential difference * current
                               = 6 * 0.75
                               =  4.5 W = 0.0045 kW
Energy consumed by the bulb in 4 hrs = Power * time  
                                                                  = 0.0045* 4
                                                                  = 0.018 kWh or 18Wh

Hope this helps you.