Suppose refractive index μ is given as μ=A+B/λ2 ? where A and B are constants and λ is wavelength, then the dimension of B is same as that of:

As, μ=Velocity of light in vacuumVelocity of light in mediumThe refractive index μ is dimensionless, so each term on right hand side is dimensionless. Hence, Bλ2 is also dimensionless. This implies that dimensions of B will have the dimensions of λ2, i.e., of area.