Question

Q. At what distance from a concave mirror of focal length 10 cm should an object 2 cm long be placed in
to get an erect image 6 cm tall ?
​

Answer 1

Explanation:

concave mirror , f is negative ,  f = -10 cm

  u = ?

h = 2 cm  

erect image  so  h' is positive,  h' = 6 cm

    so m = h'/h = 3

        as  m = -v/u = 3  => v = -3 u

  mirror equation  is  1/v + 1/u = 1/f

      1/(-3u) + 1/u = 1/(-10)

         2/(3u) = -1/10

           u = -20 /3 cm = -6.67 cm         and  v = -3 u = 20 cm

          v is positive,  so image is behind the mirror and is virtual.

 in concave mirror , an erect image is obtained when the object is between the pole and the focus. it is magnified and is virtual.  so  you can verify from values of u, v and f.