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JEE Main20257 Apr 2025Evening ShiftPhysicsRay OpticsActual

A mirror is used to produce an image with magnification of 1 4 . If the distance between object and its image is 40 cm , then the focal length of the mirror is ________

Options

  1. A10 cm
  2. B12.7 cm
  3. C10.7 cm
  4. D15 cm

Correct answer

C. 10.7 cm

Step-by-step solution

aligned & m =- v u =- ( v - u )= v u & 1 4 = v u u =4 v & v + u =40 & 5 v =40 & v =8 ~cm & u =32 ~cm & 1 v + v u = 1 f & 1 8 - 1 32 = 1 f & 4-1 32 = 1 f & f = 32 3 =10.7 ~cm aligned

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