(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.

Explanation

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)`.