Question

(ii)
An object when placed at a distance of 25 cms from a convex
lens produces a double sized real image on the other side of
the lens. Calculate :

The image distance
The focal length of the lens.​

Answer 1

Answer:

f=50cm

Explanation:

-v/u=2

1/f=1/v-1/u

=1/25-1/50

=1/50

f=50cm

Answer 2

Given

-------

u=-25 cm

magnification= - 2

To find

-----------

v=?

f=?

Solution

-------------

By lens formula,

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

_______(1)

And by magnification formula of lens,

m= v/u

-2=v/-25

v=+ 50 cm

Now, putting the values of v and u in (1)

$\frac{1}{50 } - \frac{1 }{ - 25} = \frac{1}{f}$

=>1/50+1/25=1/f

=>3/50=1/f

=>f=50/3 cm

Answer

-----------

Hence, the value of image distance is +50 cm and the value of focal length is +50/3cm.