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JIPMER2006PhysicsRay Optics

If the focal length of a lens of a camera is 5 f and that of another is 2.5 f , what is the time of exposure for the second, if for the first one is 1 200 ~s ? (where f is focal length/unit aperture)

Options

  1. A1 200
  2. B1 800
  3. C1 6400
  4. D1 3200

Correct answer

B. 1 800

Step-by-step solution

Ratio of time of expoiusers aligned & t₁ t₂ = ( f₁ f₂ )^2= ( 5 f 2.5 f )^2 & 1 / 200 t₂ =(2)^2 & t₂= 1 800 ~s & aligned

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