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 between the earth and the moon is 3.8 x 10^{5} km.

6.9 cm

the focal length of the concave mirror, f= 7.6 m

Diameter of the moon= 3450km

Since the distance of the moon from earth is very large as compared to the focal length of the mirror, so, it can be considered as infinity. When the object is at infinity the image formed will be of the focus of the mirror. Hence, the image of the moon will be formed on the focus of the mirror and it will be inverted.

Using mirror formula,

Magnification m=

Hence,

1