Find the diameter of the image of the moon formed by a spherical concave mirror of focal length 7.6 m. The diameter of the moon is 3450 km and the distance of the earth and the moon is `3.8 xx 10^5 km.`

Explanation

`u=-30cm`
`f=-20cm`
We know `1/v+1/u=1/f`
`rarr 1/v+-1/30=-1/20`
`rarr 1/v=1/30-1/2=1/60`
`rarr v=60 cm `
image of the circle si formed at a distance 60 cm in front of the mirror.
`=:. m=-v/u=R_(image)/R_(object)`
`rarr =(-60)/((-30)v)=R_(image)/R_(object)`
`rarr R_(image)=4 cm`
Radius of image of the circle is 4 cm.