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Question: Answered & Verified by Expert
Capacitance of a capacitor made by a thin metal foil is 2 μF.If the foil is folded with paper of thickness 0.15 mm, dielectric constant of paper is 2.5 and width of paper is 400 mm,the length of foil will be
PhysicsElectrostaticsJEE Main
Options:
  • A 0.34 m
  • B 1.33 m
  • C 13.4 m
  • D 33.9 m 
Solution:
2686 Upvotes Verified Answer
The correct answer is: 33.9 m 
If length of the foil is l then

C = K ε 0 · l × b d

2 × 1 0 - 6=2 · 5 × 8 · 8 5 × 1 0 - 1 2 × l × 4 0 0 × 1 0 - 3 0 · 1 5 × 1 0 - 3

l = 3 3 · 9 m

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