Arrange the following data according to the increasing order of its focal length of given double covex lens of radius of curvature of the curved surfaces and corresponding refractive index of the material
a) R1=R2=2cm μ=1.5
b) R1=20cm,R2=10cm μ=1.6
c) R1=20cm,R2=30cm μ=1.5
d) R1=20cm,R2=40cm μ=1.5