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Question
What is the angle of polarisation and obtain the equation for an angle of polarisation?
Solution
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The angle of incidence at which the reflected beam is plane polarised light is called polarising angle (ip)
Polarisation by reflection - When ordinary light is incident on the surface of a transparent medium, the reflected light is partially plane polarised.
- The extent of polarization depends on the angle of incidence.
- For a particular angle of incidence, the reflected light is found to be plane polarised.
- 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
- At polarising angle, the reflected transmitted rays are perpendicular to other.
ip + 90° + rp = 180°
rp = 90° – ip
From Snell’s law
`(sin "i"_"p")/(sin "r"_"p")` = n - Where n is the refractive index of the medium with respect to air.
- 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 ip = n
This relation is known as Brewster’s law.
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