A Pin Is Placed 10 Cm In Front Of A Convex Lens Of Focal Length 20 Cm And Refractive Index 1.5. The Surface Of The Lens Farther Away From The Pin Is Silvered And Has A Radius Of Curvature Of 22 Cm. How Far From The Lens Is The Final Image Formed?       

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A pin is placed 10 cm in front of a convex lens of focal length 20 cm and refractive index 1.5. The surface of the lens farther away from the pin is silvered and has a radius of curvature of 22 cm. How far from the lens is the final image formed?       


Correct option is

11 cm


The value of the effective focal length F is given by  




Since the convex lens with a silvered surface behaves as a concave mirror of effective focal length F, we have


Substituting these values in the mirror formula



The negative sign shows that the image is in front of the effective mirror and hence is real.    



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