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(a) How does one demonstrate, using a suitable diagram, that unpolarised light when passed through a polaroid gets polarized ? (b) A beam of unpolarised light is incident on a glass-air interface. Show, using a suitable ray diagram, that light reflected from the interface is totally polarised , when mutani_(B), where mu is the refractive index of glass with respect to air and i_(B) is the Brewster's angle. |
Answer» SOLUTION :(a)  The components of electric vector associated with light wave, along the direction of aligned molecules of a polaroid, get absorbed. As a result after PASSING through it, the components perpendicular to the direction of aligned molecules will be obtained in the form of plane polarised light. (b) When unpolarised light is incident on the BOUNDARY between two TRANSPARENT media, the reflected light is polarised, with electric vector perpendicular to the plane of incidence when the relfected and refracted light rays make a right angle, as shown in the figure below.  Since, `/_CBQ+/_QBD=90^(@)` `(90-i_(B))+(90-r)=90^(@)` `i_(B)+r=90^(@)` `r=90-i_(B)` Using Snell.s law, `mu=(sini_(B))/(sinr)` `=(sini_(B))/(SIN(90-i_(B))` `=(sini_(B))/(cosi_(B))` `mu=tani_(B)` |
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