Question

An object placed at 2F from a convex lens of focal length F, forms an image. Where is the image formed?

Answer 1

Given Convex lens
focal length f = F
position of object u = -2F
find position of image v=?
formula
1/f = 1/v -1/u
1/F = 1/v - 1/(-2F)
1/F = 1/v + 1/2F
1/F-1/2F = 1/v
2/2F -1/2F = 1/v
-1/2F = 1/v
v = -2F
so image will be formed at 2F towards side of object.