The image of the moon is focused by a converging lens of focal length 50 cm on a plane screen. The image is seen by an unaided eye from a distance of 25 cm. Find the angular magnification achieved due to the converging lens.

Explanation

Suppose the moon subtens an anle alpha on the lens. This wil also be the angle subtended by th moon on the eye if the moon is directly viewed. The image is formed i the focla plane. The linear size of the image `=falpha=(50cm)alpha`
if this image is seen from a distance of 285 cm, the ange formed by the image on the eye
`|beta|=((50cm)|alpha|)/(25cm)=2|alpha|`
the angulr magnification is
`beta/alpha=-|beta/alpha|=-2`