A thin convex lens of focal length 10 cm is placed over a plane glass mirror. An object is placed 20 cm above the lens.Find the distance of image from the object.

Dear Ajit,

The image distance after 1st refraction by the lens is=20 cm towards the plane mirror (simply from the lens formulae)

but it will get reflected from the mirror and will try to form at a distance 20 cm in front of the lens. it will then again rf\efracted by the lens and this time u=+20 cm

So again using lens formulae we get, v=20/3 cm from the lens towards the object.

Hence the distance between the image & the object will be=(20 - 20/3)cm

                                                                               =40/3 cm

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SOUMYAJIT IIT_KHARAGPUR