Question

An object at a distance of 40 cm from a concave mirror gets its image at the same point. The focal length of the mirror is​

Answer 1

f =focal length    u= distance of object=40cm    v=distance of image

                                                                               given:same as u

then

1/f=1/u+1/v

   =1/40+1/40

1/f=2/40

f=40/2

 20cm

∴focal length=20cm