The focal length of a double convex lens is equal to the radius of curvature of either surface. The refractive index of its material is;
Answer & explanation
Correct answer: option 3
1/f = (µ-1) (1/r1 + 1/r2)
For this case r1 = r2 = f
1/r = (µ-1)(1/r+1/r)
u-1= (1/r)/(1/r+1/r)
=1/2
µ(refractive index) = 1+1/2 = 3/2 = 1.5