Question

an electric lamp and a screen are placed on the tabe, in a line at a distance of 1 metre. in what positions of convex lens of focal length of f=21cm will the image of lamp be sharp ?

Answer 1

So, the image will be sharp at a distance of 21cm from the lens ,i.e, focus of the convex lens as all the rays comming from beyond the optical centre of the lens concentrate on the principle focus.

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