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In the given figure, the radius of curvature of curved surface for both the plano-convex and plano-concave lens is 10 cm and refractive index for both is 1.5. The location of the final image after all the refractions through lenses is

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Solution

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The focal length of the plano - convex lens is:

1f1=(1.5−1)(1+10−1∞)=120

Focal length of plano - concave lens is:

1f2=(1.5−1)(1∞−110)=−120

since parallel beams are incident on the lens, its image from plano - concave lens will be formed at +20 cm from it (at the focus) and will act as an object for the plano - concave lens. since the two lens are at a distance of 10 cm from each other, therefore, for the next lens

u=+10 cm

v=ufu+f=10×2010−20

⇒v=(20010) cm=20 cm

Hence, the correct option is (B)

Hence, the correct option is (B)

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