Question

a lens of focal length 20cm is used to produce a 10 times magnified image of a film slide on a screen how fare much this light be placed from the lens

Answer 1

refer the attachment for the answer

Answer 2

Answer:-

22cm

Explanation:-

Given

Focal length (f) = 20cm

size of the image(v) = 10 times the size of the object(u)

To Find

Object distance

Solution

We know that

$\boxed{\dfrac{1}{f} = \dfrac{1}{v} - \dfrac{1}{u}}$

Acc to sign convention

f = 20cm

v = 10u

u = -u

On putting the values

$\dfrac{1}{20} = \dfrac{1}{10u} - (\dfrac{1}{-u})$

$\dfrac{1}{20} = \dfrac{1}{10u} + \dfrac{1}{u}$

$\dfrac{1}{20} = \dfrac{10+1}{10u}$

$\dfrac{1}{20} = \dfrac{11}{10u}$

$u = \dfrac{11 \times 20 }{10}$

$u = 22 cm$