Explain how to produce an electric current by the relative movement of a magnet and a conductor

a) on a small scale in the laboratory
b) in the large-scale generation of electrical energy

Recall the factors that affect the size and direction of an induced potential difference, and describe how the magnetic field produced opposes the original change

Explain how electromagnetic induction is used in alternators to generate current which alternates in direction (a.c.) and in dynamos to generate direct current (d.c.)

Explain the action of the microphone in converting the pressure variations in sound waves into variations in current in electrical circuits, and the reverse effect as used in loudspeakers and headphones

Explain how an alternating current in one circuit can induce a current in another circuit in a transformer

Recall that a transformer can change the size of an alternating voltage

Use the turns ratio equation for transformers to calculate either the missing voltage or the missing number of turns:

\(\dfrac{\text{p.d. difference across primary coil}}{\text{p.d. difference across secondary coil}} = \dfrac{\text{number of turns in primary coil}}{\text{number of turns in secondary coil}}\)

\(\dfrac{V_p}{V_s} = \dfrac{N_p}{N_s}\)

Explain why, in the national grid, electrical energy is transferred at high voltages from power stations, and then transferred at lower voltages in each locality for domestic uses as it improves the efficiency by reducing heat loss in transmission lines

Explain where and why step-up and step-down transformers are used in the transmission of electricity in the national grid

Use the power equation (for transformers with100% efficiency):

potential difference across primary coil (volt, V) × current in primary coil (ampere, A) = potential difference across secondary coil (volt, V) × current in secondary coil (ampere, A)

\(V_p × I_p = V_s × I_s\)

Explain the advantages of power transmission in high-voltage cables, using the equations in 10.29, 10.31, 13.7P and 13.10