Question

The focal length of an equiconvex lens is equal to the radius of curvature of either face. what Is the refractive index of the material of the lens?

Answer 1

focal length of a lens is given by:

1/f = (u-1) (1/r1 + 1/r2)

by the iven information we have got
r1 = r2= f = r

1/r = (u -1) (1/r + 1/r) 

or

u = 1/2 + 1
= 3/2
= 1.5

Answer 2

Hey !!

→ 1/f = (μ - 1) (1/R₁ - 1/R₂)

→ 1/f = (μ - 1) (2/f)          (∴ f = R )

→ 1/2 = (μ-1)

       →  μ = 1.5

Good luck !!