Electricity and Magnetism - Practical electricity

Electrical Power ($P$): The rate at which electrical energy is transferred by a circuit. The SI unit is the Watt ($W$), where $1 W = 1 J/s$.

Electrical Energy ($E$): The total energy consumed over a period of time $t$. In domestic settings, it is often measured in kilowatt-hours ($kWh$) instead of Joules ($J$).

Mains Electricity: Most domestic supplies use Alternating Current ($AC$). In many IGCSE contexts, the standard supply is approximately $230 V$ at a frequency of $50 Hz$.

The Three-Pin Plug: Consists of the Live wire (Brown, carries high voltage), Neutral wire (Blue, completes the circuit at $0 V$), and Earth wire (Green/Yellow striped, safety wire).

Safety Components: Fuses and Circuit Breakers (MCBs) protect circuits from overheating by breaking the connection when the current exceeds a specific rating. The fuse must be placed in the Live wire.

Earthing and Double Insulation: The Earth wire provides a low-resistance path to the ground for fault currents. Appliances with plastic casings that do not require an earth wire are 'Double Insulated' and marked with the $\square$ symbol.

Cost of Electricity: Calculated by multiplying the energy used in $kWh$ by the cost per unit. $1 kWh$ is the energy used by a $1 kW$ appliance running for $1$ hour ($1 kWh = 3.6 \times 10^6 J$).