CAIE IGCSE Physics 4.2.4.3 State, qualitatively, the relationship

Practise comparing metallic wires by length and cross-sectional area, using diagrams, tables and qualitative resistance changes.

Exam points

compare wires of the same material by linking longer length to greater resistance
use larger cross-sectional area or diameter to predict lower resistance and higher current
explain why thick copper conductors reduce heating when large currents are carried

[Maximum number: 2]

The electric starter motor in a car is switched on and off using a relay.
The relay consists of a plastic case and two flexible springy strips, X and Y, which are made of soft iron. These iron strips act as the switch when a circuit is connected between the terminals W and Z.

$Fig. 7.1 shows \(\mathrm{X$

Fig. 7.1 shows \(\mathrm{X

Fig. 7.2 shows the equipment from Fig. 7.1 inside a magnetising coil. The magnetising coil is in series with the 12 V car battery and switch S , which is open.

The power of the starter motor is 1.8 kW and it is also operated by the car battery.

The starter motor circuit is connected between terminals W and Z .

Explain why copper wires with a large cross-sectional area are used for this circuit.

All question bank results loaded

4.2.4.3—State, qualitatively, the relationship question 1