State and prove Brewster's law.

Explanation

It states that when unpolarised light incident at polarising angle `i_(B)`, on an interface separating air from a medium having refractive index `mu`, then
`mu="tan"i_(B)`
Proof : Experimantally, it has been found that when light is incident at polarising angle `i_(B)`, then reflected component along OB and refracted along OC are mutually perpendicular to each other.

i.e., `angleBOY+angleYOC=90^(@)`
`rArr(90^(@)-i_(B))+(90^(@)-theta_(r))=90^(@)rArr90^(@)-i_(B)=90^(@)-90^(@)+theta_(r)`
`rArr90^(@)-i_(B)=theta_(r)`
According to Snell. law
`("sin"i_(B))/("sin"theta_(r))=murArr("sin"i_(B))/("sin"(90^(@)-i_(B)))=murArr("sin"i_(B))/("cos"i_(B))=murArr"tan"i_(B)=mu`