Electricity and Magnetism

Electricity is the flow of electric charge (electrons) through a conductor. A complete circuit — a closed loop — is needed for current to flow. Key quantities: Current (I) — rate of charge flow, measured in Amperes (A); Voltage/potential difference (V) — energy per unit charge, measured in Volts (V); Resistance (R) — opposition to current, measured in Ohms (Ω). Ohm's Law: V = IR (voltage = current × resistance). This relationship holds for ohmic conductors at constant temperature. Power: P = IV = I²R = V²/R, measured in Watts. Series circuits: components share the same current; total resistance = sum of all resistances; voltage is shared. Parallel circuits: components share the same voltage; total current = sum of branch currents; total resistance is less than any branch. Household circuits are wired in parallel so each appliance receives full mains voltage and can be switched independently.