Page 15 - Spotlight A+ Physics Form 4.5

Form
5 Physics Chapter 3 Electricity

Conclusion:
Different material has different resistivity and gives different resistance. When the resistivity of a material
increases, its resistance also increases. The hypothesis is accepted.

Assume the conductors as a road and the current as a car you are driving in. Constantan wire is as if an old road
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with potholes and badly damaged, copper is as if a newly built road and tungsten is as if uneven road. The
different road (different wires) gives you different obstructions (resistance) to drive through them. Old road
with potholes and badly damaged (constantan) is most difficult to drive through due to a lot of obstructions
(high resistance). Newly built road (copper) is easiest to drive through because it gives very little obstruction
(resistance).

CHAP
3 Application of Resistivity of Conductor in Daily life

1 Heating element

(a) Heating element is used in water heater and electric kettle to heat
up water.
(b) Heating element is usually made from material with higher
resistivity.

(c) The higher resistance enables the heating element to convert
electrical energy to heat energy to heat up the water.
(d) Other than that, heating element must also be made of:
(i) material with high melting point so that it does not melt Figure 3.29 Heating element
when heating up water,
(ii) material that can withstand oxidation so that the water heated
up is not contaminated by its oxide which is probably toxic.

2 Electrical wiring in homes

(a) Copper wires are usually used in the electrical wiring in
homes because copper have low resistivity.
(b) The low resistance of copper wire enables electrical current
to flow more efficiently by reducing the energy loss to the
surroundings in the form of heat.
(c) Other than that, copper wire can resist oxidation and do not
oxidise easily by the action of oxygen in air. Figure 3.30 Copper wires in
electrical wiring in homes
(d) Nevertheless, in the National Grid Network, aluminium
cables are used instead of copper even though the resistivity
of aluminium is higher than copper. This is because the
density of aluminium is way lower than copper. This causes
the aluminium cables to be lighter than copper cables.

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