Tungsten is a conductor used as the filament of an electric lamp. The filament of the lamp is surrounded by glass which is an insulator.

Outline, in terms of their atomic structure, the difference between the electrical properties of tungsten and of glass.

A tungsten filament lamp is marked 6.0 V, 15 W.

(i) Show that the resistance of the lamp at its working voltage is 2.4 Ω.

(ii) The length of the filament is 0.35 m and the resistivity of tungsten is 5.6×10^–7 Ω m at its working voltage.

Calculate the cross-sectional area of the tungsten filament.

The diagram shows part of a potential divider circuit used to measure the current-potential difference (I–V) characteristic of the bulb.

Draw the complete circuit showing the correct position of the bulb, ammeter and voltmeter.

conduction is due to movement of the free electrons (transferring charge around circuit);
tungsten is a good electrical conductor with large numbers of free electrons;
glass is a poor electrical conductor with few/no free electrons;

(i) \(\frac{{{6^2}}}{{15}}\) or \(I = \frac{{15}}{6}\) and \(R = 6 \times \frac{6}{{15}}\);
\( = 2.4\Omega \)

(ii) \({\rm{area}} = \frac{{5.6 \times {{10}^{ - 7}} \times 0.35}}{{2.4}}\);
0.082mm² or 8.2×10^-8m²

lamp connected so that pd can be varied;
ammeter in series with lamp and voltmeter
in parallel with lamp; (both needed)
Award [0] if lamp cannot light.