Question

A 4-kW resistance heater in a water heater runs for 2 hours to raise the water temperature to the desired level. Determine the amount of electric energy used in both kWh and kJ

Answer 1

The electric energy used by a 4-kW resistance heater running for 2 hours is 8 kWh, which is equivalent to 28800 kJ when converted.

Step-by-step explanation:

To determine the amount of electric energy used by a 4-kW resistance heater running for 2 hours, you need to multiply the power rating of the heater by the time it is in use. That is:

Energy (in kWh) = Power (in kW) × Time (in hours)

Energy = 4 kW × 2 hours = 8 kWh

Now, to convert the energy from kWh to kJ, we use the conversion factor where 1 kWh equals 3.6 × 106 J (or 3600 kJ).

Energy (in kJ) = Energy (in kWh) × 3600 kJ/kWh

Energy = 8 kWh × 3600 kJ/kWh = 28800 kJ

The electric energy used is 8 kWh or 28800 kJ.