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When a particular wave length of light is used the focal length of a convex mirror is found to be 10 ~cm . If the wave length of the incident light is doubled keeping the area of the mirror constant, the focal length of the mirror will be:

Options

  1. A20 cm
  2. B5 cm
  3. C10 cm
  4. D15 cm

Correct answer

C. 10 cm

Step-by-step solution

The focal length f of a spherical mirror is given by the relation f = R 2 , where R is the radius of curvature of the mirror. The radius of curvature R depends only on the geometry and the physical dimensions of the mirror surface. It is determined by the radius of the sphere from which the mirror is cut. The focal length of a mirror is independent of the wavelength of the incident light. Changing the wavelength of the light does not alter the physical shape or the radius of curvature of the mirror. Since the area

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