Brewster’s Law

Brewster’s Law :- (Discovered by Sir David Brewster in 1892)

The tangent of the polarizing angle is equal to the refractive index of the refracting medium at which partial reflection takes place.

Explanation :

          When Sir David Brewster performed series of experiments on the polarization of light by the reflection, he discovered that when the light is incident on a transparent medium at polarizing angle, the reflected light is completely plane polarised in the plane of incidence, and reflected rays are separated by 90⁰ from each other, then tangent of the angle at which the complete polarization is obtained by the reflection is numerically equal to refractive index of the reflecting medium.

Numerical Explanation :

        If   i_p is the polarizing angle and if µ is the refractive index of the medium then from fig.

Conclusion :

        From Brewster’s law, it follows that the polarizing angle depends on wavelength and is different for different colours. However in most transparent media it is found that the dispersion is too small to effect the polarizing angle appreciably. Brewster’s law does not hold good for polished metallic surface.