Four cubic meters of water is to be heated by means of four 1.5 kW, 230 V immersion heating elements. Assuming the efficiency of the heater as 90%, determine the time required boiling the water if the initial temperature is 20°C and if all four elements are connected in parallel.
Entering the known values of current and voltage for the hot headlight, we obtain
P = IV = (2.50 A)(12.0 V) = 30.0 W.
The cold resistance was 0.350 Ω, and so the power it uses when first switched on is
P=V2R=(12.0 V)20.350 Ω=411 W