A Plano-convex lens (focal length f2 refractive index μ2 radius of curvature R) fits exactly into a plano-concave lens (focal length f1, refractive index μ1, radius of curvature R). Their plane surfaces are parallel to each other. Then, the focal length of the combination will be

\(\frac{{\rm{R}}}{{{{\rm{\mu }}_2} - {{\rm{\mu }}_1}}}\)

\(\frac{{2{{\rm{f}}_1}{{\rm{f}}_2}}}{{{{\rm{f}}_1} + {{\rm{f}}_2}}}\)

A Plano-convex lens (focal length f2 refractive index μ2 radius of cu

1.	A Plano-convex lens (focal length f2 refractive index μ2 radius of curvature R) fits exactly into a plano-concave lens (focal length f1, refractive index μ1, radius of curvature R). Their plane surfaces are parallel to each other. Then, the focal length of the combination will be
A.	f1 – f2
B.	\(\frac{{\rm{R}}}{{{{\rm{\mu }}_2} - {{\rm{\mu }}_1}}}\)
C.	f1 + f2
D.	\(\frac{{2{{\rm{f}}_1}{{\rm{f}}_2}}}{{{{\rm{f}}_1} + {{\rm{f}}_2}}}\)
Answer» C. f1 + f2

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A Plano-convex lens (focal length f2 refractive index μ2 radius of curvature R) fits exactly into a plano-concave lens (focal length f1, refractive index μ1, radius of curvature R). Their plane surfaces are parallel to each other. Then, the focal length of the combination will be

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