An object 2 cm high is placed at a distance of 64 cm from a white screen. On placing a convex lens at a distance of 32 cm from the object, it is found that a distinct image of the object is formed on the screen. What is the focal length(f) of the convex lens, and the size of the image(hi) formed on the screen?

The focal length of the convex lens is

16 cm

, and the size of the image formed on the screen is

2 cm

.
As the object-screen distance is double the object-lens distance, the object is at a distance of

2 f

from the lens, and the image should be the same size as the object and formed at

2 f

on the screen.

\Rightarrow 2 f = 32

\Rightarrow

f = 16

Height of the image

=

height of the object

= 2 cm

Thus,

f = 16 cm;

h_{o} = h_{i} = 2 cm

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