Question

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?

Answer 1

Lens formula is

`1/v-1/u=1/f`

Where

`"object distance" (u)==-30mm`

`"focal length" (f)=+15`

`"image distance" (v)==?`

Now inserting in the eqution we get

`1/v-1/(-30)=1/15`

`=>1/v=1/15-1/30=1/30`

`=>v=30mm`

Hence magnification `(m)=v/u=30/30=1`

So the image is real and the length of 20mm side of the stamp in the image will be same, 20mm.