Question

The above image shows a thin lens with a focal length of 5m.

1. What is the kind of lens shown in the above figure?
2. If a real inverted image is to be formed by this lens at a distance of 7m from the optical centre, then show with calculation where should the object be placed.
3. Draw a neatly labelled diagram of the image formation mentioned in (ii).

Answer 1

1. Convex lens
2. `1/f = 1/v - 1/u`
   In this case, v = 7m and f = 5m
   Putting the values in the equation, we get,
   `1/5 = 1/7 - 1/u`
   `1/u = 1/7 - 1/5 = (5 - 7)/35 = (-2)/35`
   `u = -35/2 = -17.5` m
   The object will be placed 17.5 m on the left of the convex lens.
3. 
   
   (two rays, arrows, and object placed beyond 2f on the left)