An extended object is placed at the principal focus of a lens. Where will the final image be formed? Comment on the nature of the image.

Explanation

`(1)/(f)= (1)/(u)+(1)/(v)`
`(1)/(f)= (1)/(f)+(1)/(v) `
`therefore (1)/(v)=0 rArr v=oo`
The image is formed at infinity and the image will be real and inverted.