Question

An image by a concave mirror is 4times greater than the object. If the radius of curvature is 20cm,determine the object distance infront of the mirror ?​

Answer 1

Answer:

7.5 cm

Explanation:

u = Object distance

v = Image distance

f = Focal length = 20/2 = 10 cm (positive if the left side is taken as positive)

m = Magnification = 4

$m=-\frac{v}{u}\\\Rightarrow 4=-\frac{v}{u}\\\Rightarrow v=-4 u$

Lens equation

$\frac{1}{f}=\frac{1}{u}+\frac{1}{v}\\\Rightarrow \frac{1}{10}=\frac{1}{u}+\frac{1}{-4u}\\\Rightarrow \frac{1}{10}=\frac{3}{4u}\\\Rightarrow u=\frac{3}{4}\times 10\\\Rightarrow u=7.5\ cm$

Object is 7.5 cm from the mirror

Answer 2

Explanation:

hope it helps you