Question

A convex lens makes a real image 4 cm long on a screen. When the lens is shifted to new position without disturbing the object, we again get a real image on the screen which is 16 cm tall. The length of the object must be

1. 12 cm

2. 20 cm

3. 8 cm

4. 1/4 cm

Please solve the question.

Answer 1

initial image height=4cm

after changing lens position,

image height =16cm

let object length = o

by using the formula,

o=√4×16=√64=8cm

∴ correct option is 3.

Answer 2

The length of the object must be 8 cm.

Option - 3

Explanation:

we are given the image height initially to be 4 cm but later on when  the position of lens is changed.

The new height of image is given as 16 cm.

Let us take the length of object to be zero

Applying these values in the formula we shall get,

0 =$\sqrt4 \times \sqrt{16}$

=$\sqrt{64}$ = 8cm

Hence the length of the object in the image is 8 cm.

To know more:

The equi convex lens has focal length equal to the radius of curvature. Its refractive index is

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