A metallic filament lamp is connected to an ideal 12V d.c. supply. As the lamp warms up, its resistance increases appreciably.
(i) State Ohm’s law for a conductor kept at constant temperature.
(ii) Explain qualitatively, without using any numerical calculation, how the current in the circuit is affected as the filament resistance rises while the supply voltage remains unchanged.
(iii) If the resistance of the filament finally becomes double its initial value, describe and justify the consequent change in the rate at which electrical energy is converted into heat in the filament.