Question

to find the focal length of a convex lens using optical bench

Answer 1

Aim
To find, the focal length of a convex lens by plotting graphs between u and v or between 1/u and 1/v.

Apparatus
An optical bench with three uprights (central upright fixed, two outer uprights with lateral movement), a convex lens with lens holder, two optical needles, (one thin, one thick) a knitting needle and a half metre scale.

Theory
The relation between u, v and f for a convex lens is
to-find-the-focal-length-of-a-convex-lens-by-plotting-graphs-between-u-and-v-or-between-1u-and-1v-1
where,
f = focal length of convex lens
u = distance of object needle from optical centre of the lens
v = distance of image needle from optical centre of the lens.
Note. According to sign-convention, u has negative value and v has positive value
Hence,f comes positive

Answer 2

Answer:

To determine focal length of a convex lens

Place the holder with the screen on the bench. The position of the screen should be such that the sharp image of the distant object is obtained on it. The difference between the position of the lens and the screen is equal to the focal length of the given convex lens.