Question

In a concave mirror when the object is placed at 20 cm from mirror, it forms an image at 20 cm in front of it. What is the focal length of the mirror?​

Answer 1

Answer:

Given : Object distance, u=−20 cm

A concave mirror forms a real magnified image only when the image to be formed is inverted i.e. m=−3

Magnification m= - v/u

∴ --3=--v/--20

⟹v=−60 cm

Using mirror formula : 1/v+1/u= 1/f

∴ 1/--60+1/--20=1/f

⟹ f= --60/4 =−15 cm

Thus focal length of the mirror is 15 cm.

Answer 2

Answer:

given,

u= -20cm

v= 20

soln

1/v+1/u = 1/f

1/20 - 1/20=1/f

1/f=0

f=0

Explanation:

its an easy math i did accordong to formulae hope u will understand