Question

The real image of an object is formed at a distance of 90 cm from a concave mirror of focal length 15 cm

Answer 1

given:-

V=image distance = -90cm

focal length= -15 cm

We have to find

u=object distance

using mirror formula,

1/f=1/v+1/u

1/(-15)=1/(-90)+1/u

1/(-15)+1/(90)=1/u

-6+1/90=1/u

1/(-18)=1/u

u=-18cm

so the object distance is -18 cm.