Soumendra M. answered 02/11/15
Learn and Enjoy Math-Phy-CS-EE
relative refractive of glass index in water = ng/nw = 1.1428
Formula associating focal length with Radii of two surfaces: 1/f = (n-1) (1/R1 - 1/R2)
(1/R1 - 1/R2) is constant for a lens,
f2/f1 = (n1-1)/(n2-1)
Here n1 = 1.52, n2 = 1.14286, f1 = 40cm, f2 = ?
f2 = f1 * (n1 - 1) /(n2 -1) = 40 *.52 /.14286 = 145.597 cm