Question

Rohit placed a pencil perpendicular to principal axis in front of coverging mirror of focal length 30cm.The image formed is twice the size of pencil. calculate distance of obj from mirror​

Answer 1

Magnigfication = hi / ho = -v / u

We can assume it to be virtual because in a concave mirror, it is enlarged only when it is virtual. Otherwise, if you refer to the ray diagrams, they are all diminished.

The remaining procedure is correct, wherein we get -v /u = 2

So, if v = - 2u.

Using the mirror equation, 

1 / v + 1 / u = 1 /f

= -1 / 2u + 1 / u = 1 / -30

u = - 15 cms. which is between the focal length and the mirror. This proves that the image will be virtual and enlarged.