How do you find radius of curvature in achromatic lens if focal length and diameter is given?

Answer 1

You also need to know the index of refraction. For glass, that is usually somewhere around 1.5.

The Wikipedia article on "Lens (optics)" includes the "Lensmaker's equation"; usually you can use the "thin lens equation" (further down in the article) as a convenient approximation.

Since for this question you don't know the radius of curvature, and the equation includes two radii of curvature (for the two surfaces), I suggest that you make one of the following simplifying assumptions:

1) Either assume that the lens has two surfaces of equal curvature (note: for the equation in the Wikipedia article, the signs would be opposite for both sides),

2) Or, assume that the lens has one flat side and one curved side.