Question

A small insect is placed 3.75 cm from a +4.00 −cm -focal-length lens. Calculate the angular magnification.

Answer 1

Explanation:

It is given that,

Object distance, u = -3.75 cm  (negative always)

Focal length, f = +4 cm

We need to find the angular magnification of the lens. Firstly, we will find the image distance using lens formula as :

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

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

$\dfrac{1}{v}=\dfrac{1}{4}+\dfrac{1}{(-3.75)}$

v = -60 cm

Angular magnification is as the ratio of image distance to the object distance i.e.

$m=\dfrac{v}{u}$

$m=\dfrac{-60\ cm}{-3.75\ cm}$

m = +16

So, the angular magnification of the insect is 16. Hence, this is the required solution.