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

The image will be formed at focus because object is at large distance.
The angle subtended by diameter of moon at pole
`tantheta=(D)/(L)`, since `theta` is small, `tantheta=theta=(D)/(L)` radian By similar Deltas
`theta=(d)/(f)=(D)/(L)`
`d=ftheta=f .(D)/(L)=7.6xx(3450)/(3.8xx10^5)=0.069m=6.9cm`
d: diameter of image of moon.