First slide
Ray optics

A piano convex lens fits exactly into a piano concave lens. Their plane surfaces are parallel to each other. If lenses are made of different materials of refractive indices μ1 and μ2 and R is the radius of curvature of the curved surface of the lenses, then the focal length of the combination is


The combination of two lenses 1 and 2 is as shown in figure.


According to lens maker's formula

1f1=μ1111R=μ11R 1f2=μ211R1 =μ211R=μ21R   1f=μ11Rμ21R 1f=μ1μ2R f=Rμ1μ2

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