A typical electric water heater has a heating element rated

A typical electric water heater has a heating element rated at 4500 Watts and is connected across a 240 Volt power source. When operated normally, find the resistance of the heating element, the current drawn by the heating element, and the cost of heating water for 45.0 minutes. Assume electricity costs $.10/kw * hr.

Solution

Power P = 4500 W

Voltage V = 240 volt

We know P = V ²/ R

From this resistance R = V ² /P

                                  = 240 ² / 4500

                                  = 12.8 ohm

(b). Current i = P/V

                   = 4500 / 240

                   = 18.75 A

(c).Time t = 45 min = (45/60) h    Since 1 h = 60 min

                             = 0.75 h

Energy E = Pt

               = 4500W (0.75 h)

                = 3375 Wh

                = 3.375 kW h

Electricity cost = 3.375 kW h ($.10 /kW h)

                       = $0.3375