Question

Three students measured the focal length of a convex lens using parallel rays from distant object. All of them measured the distance between the lens and the inverted image on the screen. Student A saw a sharp image on the screen and labelled the distance as f₁. Student B saw a slightly larger blurred image on the screen and labelled the distance as f₂. Student C saw a slightly smaller blurred image on the screen and labelled the distance as f₃. What is the relation between the three measurements?

Answer 1

A sharp image is formed at focus. A slightly blurred larger image is formed beyond the focus and a slightly blurred smaller image is formed before the focus.

Therefore, f₃ < f₁< f₂.