A double-convex lens is to be made of glass with an index of refraction of 1.5. One surface is to have twice the radius of curvature of the other and the focal length is to be 60 mm. We have to find the radii.
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Solution: Click For PDF Version The focal length f of lens is given by the relation
where
We can solve for from the equation
Therefore, the radii of the double-convex lens are 45 mm and 90 mm. |
and
are the radius of curvature of the first and the second curved
surfaces of the lens. In a convex lens the centre of curvature of
the first curved face,
,
lies in the R-side
and therefore the radius of curvature
is positive. The centre of curvature of the second face of the
double-convex lens,
,
lies in the V-side
and therefore the radius of curvature
is negative.