Exam-style question
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What happens to the resistance of a filament lamp as it warms up during operation?.
- A.It decreases.
- B.It stays the same.
- C.It increases.
- D.It fluctuates randomly.
Model answer
What a good answer should say
- It increases.
Explanation
Why this works
The resistance of tungsten rises with temperature. As the lamp is powered, the filament heats, its resistance increases, and the current for a given applied voltage decreases.
This temperature dependence explains the non‑linear I‑V characteristic of a hot filament lamp.
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