Is given by Power = current x voltage Watts (J/sec) = Amperes (C/sec) x Volts (J/C) Isn"t that simple???? If a 120-V line to a socket is limited to 15 A by a safety fuse (or circuit breaker), will it operate a 1200-W hair dryer? Will it operate two hair dryers? At 10/kW-hr, what does it cost to operate the 1200-W hair dryer for 1 hr? Note: 1 kW = 1000 W = 1000 J/s. What is the resistance of the filament in a 75W light bulb? First, what"s the AC line voltage (in the US)? Then, how much current to give 75W? (power = voltage x current) Finally, what"s the resistance?