Question

a concave mirror has a focal length of 20cm at what distance from the mirror should a 4 cm tall object be placed so that it forms an image at a distance of 30 cm from the mirror also calculate the size of the image formed

Answer 1

Was I coming -60 and ht of image 2 cm?

Answer 2

Answer: The height of the image is -2 cm.

Explanation:

Given that,

Focal length f = 20 cm

Height of the object h = 4 cm

Distance of the image v = 30 cm

Using mirror formula

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

$\dfrac{1}{-20}=\dfrac{1}{-30}+\dfrac{1}{u}$

$\dfrac{1}{u}=\dfrac{1}{-60}$

$u = -60 cm$

The magnification is

$m = \dfrac{h'}{h}=-\dfrac{v}{u}$

$\dfrac{h'}{4}=-\dfrac{-30}{-60}$

$h' = -2 cm$

Hence, The height of the image is -2 cm.