Question

A small object is so placed in front of a convex lens of 5 cm focal length that a virtual image is formed at a distance of 25 cm. Find the magnification

Answer 1

I/f=1/v-1/u
1/5=1/-25-1/u
-1/25-1/5=1/u
(-1-5)/25=1/u
-6/25=1/u. U=-25/6
Magnification=v/u
-25/(-25/6)=6

Answer 2

Then the magnification is 6.

Given data:

The lens given is a convex lens

Focal length f = 5 cm

The image formed is virtual so v = -25 cm.

Solution:

Using the lens formula, we can find the value of magnification

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

Substituting the values in the equation

$\frac{1}{5}=\frac{1}{u}-\frac{1}{25}$

u = 4.167 cm

To find magnification we have to use the relation

$m=-\frac{v}{u}$

Where m is the value of magnification

Substituting the value

$\begin{array}{l}{m=-\frac{-25}{4.167}} \\ {\mathrm{m}=6}\end{array}$

Therefore the image will be twice bigger as that of the object.