Question

A convex lens forms an image at 30 cm from lens on a screen.if the focal length of lens is 20 cm, find the distance at which the object is placed


please give solutions​

Answer 1

$\dagger\mathbb\red{QUESTION: }†$

A convex lens forms an image at 30 cm from lens on a screen.if the focal length of lens is 20 cm, find the distance at which the object is placed

$\dagger\mathbb\purple{SOLUTION : -60 }†$

Given:

image distance of convex lens = 30cm

Focal length of the lens = 20cm

To find:

object distance = ?

step by step explanation:

we have :

f = 30 , v = 20 and u = ?

to find u we need to:

$\bigstar★ {\green{\underline{\mathrm{\blue{formula \: =\frac{1}{f} = \frac{1}{v} - \frac{1}{u} }}}}}$

$\sf \red{\frac{1}{30} = \frac{1}{20} - \frac{1}{u}}$

$\sf \red{ \frac{1}{u} = \frac{1}{20} - \frac{1}{30}}$

$\sf \red{ \frac{1}{u} = \frac{20 - 30}{30 \times 20} }$

$\sf \red{ \frac{1}{u} = \frac{ - 10}{600} }$

$\sf \red{ \frac{1}{u} = \frac{ - 1 {\cancel{0}}}{60 {\cancel{0}}} }$

$\sf \red{ {u} = - 60 }$

Therefore:

Object should be place at a distance of 60 cm on the left side of the convex lens.

Answer 2

Explanation:

Given:

image distance of convex lens = 30cm

Focal length of the lens = 20cm

To find:

object distance = ?

step by step explanation:

we have :

f = 30 , v = 20 and u = ?

to find u we need to:

1/f=1/v-1/u

1/30=1/20-1/u

u=-60

Therefore:

Object should be place at a distance of 60 cm on the left side of the convex lens