Question

A body is located on a wall it's image of equal size is to be obtained on aparellel wall with a help of convex lens if the lens is placed at a distance of 20cm ahead of 2nd wall then what will be the required focal len

Answer 1

A body is located on a wall. It's image of equal size is to be ibtained on a parallel wall with the help of a convex lens. The lens is placed at a distance d ahead of second wall. Then the required focal length will be- 1.

Answer 2

Answer:

10 cm

Explanation

Here the image size (hi) and object size (ho) are equal.

hi = ho

In a lens--- hi/ho = v/u (v and u are image and object distance respectively)

hi/ho = 1

v/u = 1

In a lens - 1/v - 1/u = 1/f --------(1)  (f is the focal length)

1 = v/u  ,  v = u  -------- (2)

applying (2) in (1)   v = 20 cm

1/v - (-1/u) = 1/f    (u is negative, sign convention)

2/20 = 1/f

1/10 = 1/f

10 cm = f