- The power of an appliance is:
The amount of energy transferred (by electrical work) to the device every second
The power consumption of an electrical appliance can be found on a label that looks like this. This kettle uses between 2500 and 3000 W of electrical energy
- This energy is commonly measured in kilowatt-hour (kW h), which is then used to calculate the cost of energy
- This is used to calculate electricity bills
- A kilowatt-hour is defined as:
A unit of energy equal to 1 kW of power sustained for 1 hour
Energy (kW h) = Power (kW) × Time (h)
- Since the usual unit of energy is joules (J), this is the 1 W in 1 s
- Therefore:
1 kW h = 1000 W × 3600 s = 3.6 × 106 J
- Since 1 kW = 1000 W and 1 h = 3600 s
- To convert between Joules and kW h:
kW h × (3.6 × 106) = J
J ÷ (3.6 × 106) = kW h
- The kW h is a large unit of energy, and mostly used for energy in homes