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(a) How does one demonstrate, using a suitable diagram, that unpolarised light when passed through a Polaroid gets polarised? (b) A beam of unpolarised light is incident a glass-air interface. Show using a suitable ray diagram, that light reflected from the interface is totally polarised, when mu=tani_(B), when mu is the refractive index of glass with respect to air and i_(B), is the Brewster's angle. |
Answer» Solution :Condition : The reflected ray is totally plane polarised, when reflected and refracted rays are perpendicular to each other.  If `i_p`is angle of incidence, r' is angle of reflection and r the angle of refraction, then according to law of reflection `i_p=r'` and form fig, `r'+90^@+r=180^@` `rArr i_p+r=90^@`...(i) `rArr r=(90^@-i_p)` ...(II) From SNELL’s law, refractive index of second MEDIUM realstive to first medium (air) say. `n=(sin i_p)/(sin r)=(sin i_p)/(sin(90^@-i_p))=(sin i_p)/(cos i_p)` `rArr n =TAN i_p` `therefore ` Angle of incidence , `i_p=tan^(-1)(n)`. |
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