An object and the image obtained from the lens are as given above.
If the distance between the object and the image is 36 cm and the magnification is -2, find the focal length of the lens and draw the ray diagram to show the position of the lens.

Explanation

(i) The magnification , `m = v/u`
`:.` v=mu (1)
The distance between object and the image
= v + u (2)
From (1) and (2) determine the object distance 'u'.
By substituting the value value of u in one of the equations, determine the value of 'v'.
Now the focal length can be determined as
`1/f = 1/v - 1/u` (3)
(Take sign convention for only 3rd equation ).
Identify the lens used from the nature of the image formed and draw ray diagram.
(ii) 8 cm