Thin lens(urgent)

Thin lens(urgent)
1.A plano-convex lens having a focal length of 250mm is to be made of glass of refractive index n =1.520. Calculate the radius of curvature of the grinding and polishing tools that must be used to make this lens.
(1/f) = (n – 1)(1/R)
1 / 250 = (1.520 – 1)(1/R)
R = (1.520 – 1) x 250
R = 130mm

2.The radii of both surfaces of an equiconvex lens of index 1.60 are equal to 80mm. Find its power.
(1/f) = (n – 1)[(1/R1) + (1/R2)]
(1/f) = (1.6 – 1)[(1/80) + (1/80)]
f = 66.7mm = 0.0667m
power = 1/f = 1 / 0.0667
= 15D