alleryStart learning →Why does an incandescent headlight draw far more current in the first moments after it is switched on?
AIts resistance is lower when cold
BIts resistance is higher when cold
CIts supply voltage is higher when cold
DIts power rating drops when it is cold
Answer & Solution
Correct answer: A. Its resistance is lower when cold
1. Resistance of a metal filament rises as its temperature rises.
2. A bulb that has just been switched on is still cold, so its resistance is at its lowest.
3. With the supply voltage fixed, I = V / R is largest when R is smallest, so the inrush current is large.
4. As the filament heats, its resistance climbs and the current settles to the steady operating value.
5. The supply voltage does not change during warm-up, so option three misplaces the cause.
_Source: OpenStax College Physics (CC BY 4.0), Ch 20 "Electric Current, Resistance, and Ohm's Law", section Resistance and Simple Circuits_
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