Everyday electrical appliances are designed to transfer energy. The energy comes from a battery or from the ac mains. A kettle or toaster is a heating device, and it transfers energy from the mains to the thermal store of the water or the bread. A fan or a hairdryer has a motor, and the motor transfers energy to the kinetic store of the moving blades. A hairdryer does both, because it also has a heater.
The amount of energy an appliance transfers depends on its power and on how long it is switched on. The equation is energy transferred = power × time, or E = P t, with energy in joules (J), power in watts (W) and time in seconds (s). A 2000 W kettle switched on for 60 s transfers 2000 × 60 = 120000 J.
A higher power rating means more energy is transferred every second. So a 2000 W kettle changes the energy stored in the mains supply and in the water far faster than a 500 W toaster does.
Work is done when charge flows in a circuit. The energy transferred is also given by energy transferred = charge flow × potential difference, or E = Q V. Charge flow is in coulombs (C) and potential difference is in volts (V). For example, 20 C of charge flowing through a potential difference of 6 V transfers 20 × 6 = 120 J.