Question

how far should an object be from the pole of a concave mirror of focal length 20 cm to form a real image whose size is 1/5th of the size of the object​

Answer 1

Answer:

answer = 120 cm

Explanation:

given,

Focal length(f)=-20

Magnification(m)= -1/5

Object distance(u)= ?

We know

m=-v/u

-1/5=-v/

-u=5v

Now

1/t=1/v+1/u

-1/20=1/0+1/5v

-1/20=5+1/5v

-1/20=6/5v

-5v-120

-v=120/5

Therefore v=-24

Now putting the value of v in .,we get. u=5-24=-120 cm

Thus the object should be placed at 120 cm in front of the mirror

I hope it will help you...