Aaconverging lens of focal length 15 mm is used as a magnifying glass for inspecting stamp. A rectangular stamp which is 20mm 40mm is placed 30mm from the lens find the length of the image of the 20mm side of the stamp?
Lens formula is
Now inserting in the eqution we get
So the image is real and the length of 20mm side of the stamp in the image will be same, 20mm.