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The plane face of a plano convex lens is silvered.If `mu`be the refrative index and R, the radius of curvature of curved suraface, then system will behave like a concave mirror of curvatureA. `muR`B. `R^(2)//mu`C. `R//(mu-1)`D. `(mu+1)//(mu-1)R` |
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Answer» Correct Answer - c when an object is placed in fron of such a lens the rays frst of all refracted from the convex surface, then refract from the polished plane surface and again refracts from conved surface.If `F_(1) and F_(m)` be the focal lengths of lens (conved surface) and mirror (plane poplished surface) respectively then effective focal length f is given by `(1)/(f)=(1)/(F_(1))+(1)/(f_(m))+(1)/(F_(1))=(2)/(F_(m))=(2)/(f_(1)) (therefore F_(m))=R/2=oo)` `(1)/(f_(1))=(mu-1)((1)/(R))` `therefore (1)/(f)=(2(mu-1))/(r)or F=(R)/(2(mu-1))orR=2F=(R)(mu-1)` |
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