Current and voltage are the core quantities used to describe how charge moves in electrical circuits. Current is the rate at which electric charge flows, measured in amperes, and it tells you how much charge passes a point each second. Voltage, or potential difference, represents the energy transferred per unit charge as it moves between two points in a circuit. Studying these together allows you to understand how components behave, how energy is supplied and used, and how circuit laws like Ohm’s law relate current, voltage, and resistance. This topic forms the basis for analysing series and parallel circuits, power calculations, and the operation of real electrical devices. 

Current and voltage are the core quantities used to describe how charge moves in electrical circuits. Current is the rate at which electric charge flows, measured in amperes, and it tells you how much charge passes a point each second. Voltage, or potential difference, represents the energy transferred per unit charge as it moves between two points in a circuit. Studying these together allows you to understand how components behave, how energy is supplied and used, and how circuit laws like Ohm’s law relate current, voltage, and resistance. This topic forms the basis for analysing series and parallel circuits, power calculations, and the operation of real electrical devices. 

Potential difference (p.d.) and electromotive force (emf) are central ideas for analysing complete electrical circuits. Potential difference is the energy transferred from the charge to the components per unit charge as it moves through part of a circuit. It tells you how much energy is delivered to devices like resistors, lamps, or motors. Emf, on the other hand, is the energy supplied to the charge by a source such as a cell or power supply. It represents the total energy given to each coulomb of charge to push it around the circuit. In this topic you learn how emf divides across internal resistance, how terminal p.d. varies with load, and how conservation of energy ensures that the total emf equals the sum of potential differences around a closed loop. These ideas allow you to analyse real power sources and understand why ideal and non-ideal cells behave differently in practical circuits.