Charge, current, e.m.f., p.d. and resistance

Learning objectives

Describe positive and negative charge, the forces between charges, charging by friction as a transfer of electrons, and simple experiments to produce and detect electrostatic charge

Distinguish electrical conductors from insulators using a simple electron model and, at Extended, describe an electric field as a region where a charge experiences a force and sketch the field patterns around a point charge, around a charged conducting sphere and between oppositely charged parallel plates

Know that current is related to the flow of charge, compare direct and alternating current and use ammeters correctly, and at Extended define current as the rate of flow of charge, use I = Q/t and distinguish conventional current from electron flow

Define e.m.f. as the electrical work done by a source per unit charge and p.d. as the work done per unit charge passing through a component, both in volts and measured with a voltmeter, and at Extended use E = W/Q and V = W/Q

Define resistance, use R = V/I, describe an experiment to measure the resistance of a component with an ammeter and voltmeter, and at Extended sketch and explain the current–voltage graphs of an ohmic resistor, a filament lamp and a diode

Describe how the resistance of a wire depends on its length and cross-sectional area, and at Extended use the proportional relationships in calculations