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) 15 cm in front of the mirror

(b) 30 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



Rays from the sun can be considered parallel wrt the mirror. 

  • Parallel rays converge at the focus in a concave mirror. 
  • Since parallel rays are converging at 15cm after reflection from the mirror, the focus is at 15cm in front of the mirror. 
  • In case of a concave mirror, an image with magnification 1 is produced when the object is placed at its centre of curvature (C).
  • The centre of curvature of the given mirror is at 30 cm in front of the mirror.


So, the correct answer is (b)

  1. Class 10
  2. Chapter 10 Class 10 - Light - Reflection and Refraction (Term 1)

About the Author

CA Maninder Singh's photo - Founder at Teachoo
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