Question

Q19.(i) The following figures show the path of light rays through three lenses marked L1,L2 and L3 and their focal points F1, F2 and F3, respectively.

Out of L1, L2 and L3 lens/lenses is/are
(a) only L1(b) only L2
(C) only L3(d) Both L1 and L3​

Answer 1

Answer:

correct option is d.

both L1 and L3

Answer 2

Out of L1, L2 and L3 concave lens/lenses is/are (b) only L2.

• In the case of lens L1, a ray parallel to the principal axis is refracted by the lens L1 and it crosses through the principal focus of the other side of the lens. This phenomenon takes place in a convex lens.
• In the case of lens L2, a ray of light parallel to the principal axis is refracted by the lens such that it appears to meet the focus on the same side of the lens, if extended backwards. This phenomenon takes place in a concave lens.
• In the case of lens L3, a ray of light intersecting the focus is refracted by the lens such that it becomes parallel after refraction. This happens in a convex lens only.

In the concave lens, the refracted ray is parallel to the principal axis when the incident ray appears to meet the focus.