Answer:
(i) Pure tungsten has a
high resistivity and a high melting point (nearly 3000°C). When an electric
current is passed through the filament, the electric energy is converted to
heat and light energy due to the heating of the filament to a very high
temperature. Due to the high melting point of tungsten, the filament does not
melt.
(ii) The
resistivity of an alloy is generally higher than that of its constituent metals.
Alloys do not oxidise (burn) readily at higher temperatures. Therefore,
conductors of electric heating devices such as toasters and electric irons are
made of an alloy rather than pure metal.
(iii) The
series arrangement is not used for domestic circuits because:
(a) if connected in series total resistances will
increase. Therefore, current flowing through the circuit will be low.
(b) if one appliance is switched off or gets damaged than
all other appliances will also stop working because their electricity supply
will be cut off.
(iv) The
resistance of a wire is inversely proportional to its cross-sectional area. Thus,
a thick wire has less resistance, and a thin wire has more resistance.
(v)
Copper and aluminium wires are usually employed for electric energy transmission
because copper and aluminium have very low resistivities.
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