Rays from Sun converge at a point 15 cm in front of a concave mirror. Where should an object be placed so that size of its image is equal to the size of the object? 

(A) 30 cm in front of the mirror 

(B) 15 cm in front of the mirror 

(C) Between 15 cm and 30 cm in front of the mirror 

(D) More than 30 cm in front of the mirror 

Answer - 

Since rays converge at a point 15 cm from the mirror, then, focal length is 15 cm .

Also, it is concave mirror, focal length will be negative.

 

Thus,  

Focal length = f = -15 cm

Radius of Curvature = C = -30cm  

 

For a Concave mirror

  • An object kept at C makes an image of the same size as object
  • Thus, the object should be kept at C

concave-mirror---object-at-center-of-curvature---teachoo.jpg

So, the correct answer is (a)

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About the Author

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CA Maninder Singh
CA Maninder Singh is a Chartered Accountant for the past 11 years and a teacher from the past 11 years. He teaches Science, Accounts and English at Teachoo