A metal filament lamp is connected to a steady supply

PHYSICS · Single correct · CBSE · Physics · Current Electricity · Current Electricity

Problem

A metal filament lamp is connected to a steady 6 V6\,\text{V} supply. The current through the lamp decreases from 0.50 A0.50\,\text{A} just after switching on to 0.25 A0.25\,\text{A} after the filament becomes white-hot. Which statement best explains this change? (a) The supply voltage falls as the lamp warms, so with the filament’s constant resistance the current decreases. (b) The resistance of the filament decreases when hot, therefore a smaller current flows after heating. (c) The resistance of the filament rises sharply with temperature, so even at constant 6 V6\,\text{V} the current falls as the lamp heats up. (d) Ohm’s law predicts the current should stay at 0.50 A0.50\,\text{A}; the drop to 0.25 A0.25\,\text{A} indicates the ammeter is faulty.

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