kk w wt Q Figure 10 23 b shows light reflected from a transparent medium say water As before the dots and arrows indicate that both polarisations are present in the incident and refracted waves We have drawn a situation in which the reflected wave travels at right angles to the refracted wave The oscillating electrons in the water produce the reflected wave These move in the two directions transverse to the radiation from wave in the medium i e the refracted wave The arrows are parallel to the direction of the reflected wave Motion in this direction does not contribute to the reflected wave As the figure shows the reflected light is therefore linearly polarised perpendicular to the plane of the figure represented by dots This can be checked by looking at the reflected light through an analyser The transmitted intensity will be zero when the axis of the analyser is in the plane of the figure i e the plane of incidence When unpolarised light is incident on the boundary between two transparent media the reflected light is polarised with its electric vector perpendicular to the plane of incidence when the refracted and reflected rays make a right angle with each other Thus we have seen that when reflected wave is perpendicular to the refracted wave the reflected wave is a totally polarised wave The angle of incidence in this case is called Brewster s angle and is denoted by ig We can see that i is related to the refractive index of the denser medium Since we have i r 2 we get from Snell s law R R 90 siniB sinr siniB sin 2 iB