(i) Draw a ray diagram to show the path of the refracted ray in each of the following cases : A ray of light…
(i) Draw a ray diagram to show the path of the refracted ray in each of the following cases :
A ray of light incident on a concave lens
(1) parallel to its principal axis, and
(2) is directed towards its principal focus.
(ii) A 4 cm tall object is placed perpendicular to the principal axis of convex lens of focal length 24 cm. The distance of object from the lens is 16 cm. Find the position and size of image formed.
Solution
(a)(i)
(1) Ray diagram: incident ray parallel to principal axis through a concave (diverging) lens refracts as if diverging from focus F1 on the same side (Fig.9.13(b), NCERT page 153).
(2) Ray diagram: incident ray directed towards the far focus F2 emerges parallel to the principal axis in a concave lens (Fig.9.14(b), NCERT page 154).
(Note:- Deduct half mark if directions of rays are not shown)
(ii) Given u = –16 cm, f = +24 cm, h = 4 cm
Formula used $\dfrac{1}{v}$ – $\dfrac{1}{u}$ = $\dfrac{1}{f} \dfrac{1}{v}$ – 1/(–16) = 1/(+24)
$\dfrac{1}{v}$ = –1/48
v = – 48 cm
Image is formed on the same side as the object
m = h'/h = v/u
h'/4 = –48/–16
h' = 12 cm