Electric cells, current and circuits

Learning objectives

Define electric current as the rate of flow of charge, I = Δq/Δt, and relate it to the drift speed of the charge carriers using I = nAvq

Define potential difference and electromotive force as energy transferred per unit charge, and distinguish the emf of a cell from its terminal potential difference

Apply Ohm's law V = IR, calculate resistance from resistivity using R = ρL/A, and identify ohmic and non-ohmic behaviour from the I–V characteristics of a metal wire at constant temperature, a filament lamp and a diode

Calculate electrical power and energy from P = VI = I²R = V²/R, and determine the energy transferred and its cost over a stated period of operation

Analyse series and parallel combinations of resistors and of cells, applying conservation of charge at a junction and conservation of energy around a complete loop

Explain how the internal resistance of a cell reduces the terminal potential difference as current increases, and analyse a potential divider circuit including one containing a thermistor or a light-dependent resistor