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Question: Answered & Verified by Expert
A biconvex lens of focal length f forms a circular image of sun of radius r in focal plane. Then?
PhysicsRay OpticsNEET
Options:
  • A πr2 ∝ f
  • B πr2 ∝f2
  • C If lower half part is covered by black sheet, then area of the image is equal to πr22
  • D If f is doubled, intensity will increase
Solution:
2084 Upvotes Verified Answer
The correct answer is: πr2 ∝f2
r = radius of sun's image

tan⁡θ=rf=const

∴     πr2 ∝f2

Intensity only depends on the number of rays forming the image. Also only two rays are sufficient to form an image.

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