Exam-style question
Try this first
Which of the following best explains why a filament lamp has a higher voltage drop when it is hot?.
- A.The filament expands, increasing its cross‑sectional area.
- B.The filament’s resistance decreases, allowing more current to flow.
- C.The filament’s resistance increases, requiring a higher voltage to maintain the same current.
- D.The filament’s resistance stays constant, but the battery voltage rises.
Model answer
What a good answer should say
- The filament’s resistance increases, requiring a higher voltage to maintain the same current.
Explanation
Why this works
Ohm’s law (V = I × R) shows that for a fixed current, an increase in resistance demands a higher voltage. A hot filament lamp has a higher resistance than a cold one, so a larger terminal voltage is needed to drive the same current, giving the observed higher voltage drop.
Common mistake
No common mistake is linked to this question yet.