# Physica

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A contact lens is made of plastic with an index of repraction of 1.5 , The lens has an outer radius of eurvature ( convex) of 2 cm and an inner radius of curvature (concave ) of 4 cm .the focal length of the lens is;

• Physica -

1/F=(n-1) • (1/R1-1/R2)=
=(1.5-1) • (1/0.02-1/0.04)=
=0.5• (50-25)=12.5
F=0.08 m

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