Question

Where should an object be placed in front of a convex lens of focal length of 0.12m to obtain a real image of size three times the size three times the size of the object,on the screen?

Answer 1

Let the object position is "x" in front of lens for which a real image is formed on screen

The magnification of image is 3 times which means the ratio of image distance and object distance is 3

so we will have

image distance = 3* object distance

now by lens formula

$\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$

now by the lens formula we have

$\frac{1}{3x} - \frac{1}{-x} = \frac{1}{0.12}$

$\frac{4}{3x} = \frac{1}{0.12}$

$x = 0.16 m$

so object must be placed at distance 0.16 m in front of lens

Answer 2

Answer:

f= 0.12cm

m=v/u

so,v= - 3u

wkt

1/f=1/v - 1/ u

1/0.12 =1/- 3u -1/u

1/0.12 = -4u/3u

-0.48 = 3u

u = -0.16 m