Question

What is the angle of polarisation and obtain the equation for an angle of polarisation?

Answer 1

1. The angle of incidence at which the reflected beam is plane polarised light is called polarising angle (ip)
   
   Polarisation by reflection

2. When ordinary light is incident on the surface of a transparent medium, the reflected light is partially plane polarised.
3. The extent of polarization depends on the angle of incidence.
4. For a particular angle of incidence, the reflected light is found to be plane polarised.
5. The angle of incidence at which a beam of unpolarised light falling on a transparent surface is reflected as a beam of plane polarised light is called polarising angle or Brewster’s angle. It is denoted by i
6. At polarising angle, the reflected transmitted rays are perpendicular to other.
   i_p + 90° + r_p = 180°
   r_p = 90° – i_p
   From Snell’s law
   `(sin "i"_"p")/(sin "r"_"p")` = n
7. Where n is the refractive index of the medium with respect to air.
8. Substitute the value of r from Equation, we get,
   `(sin"I"_"p")/(sin (90^circ - "i"_"p")) = (sin "i"_"p")/(sin "r"_"p")` = n
   tan i_p = n
   This relation is known as Brewster’s law.