A lens having focal length f and aperture of diameter d forms an image of intensity I

A Lens Having Focal Length F And Aperture Of Diameter Physics QuestionA Lens Having Focal Length F And Aperture Of Diameter Physics Question

A lens having focal length f and aperture of diameter d forms an image of intensity I. Aperature of diameter d/2 in central region of lens is covered by a black paper. Focal length of lens and intensity of image now will be respectively:

Options

(a) f and I/4
(b) 3f/4 and I/2
(c) f and 3I/4
(d) f/2 and I/2

Correct Answer:

f and 3I/4

Explanation:

By covering aperture, focal length does not change. But intensity is reduced by 1/4 times, as aperture diameter d/2 is covered.
I’ = I – I / 4 = 3I / 4
New focal length = f and intensity = 3I / 4

AddThis Website Tools
admin:

Related Questions

  1. A block of mass 0.50 kg is moving with a speed of 2.00 ms⁻¹ on a smooth surface.
  2. A cell of emf E and internal resistance r supplies current for the same time
  3. Mass defect is known as
  4. If two bodies are projected at 30⁰ and 60⁰ respectively with the same velocity, then
  5. In a transistor, the value of βis 100, then the value of α will be