Brewster’s law of polarization

1. BREWSTER’SLAWOF
POLARIZATION
~by Shivam Sharma

2. Brewster’s Law
Relationship for light waves states that the maximum
polarization (vibration in one plane only) of a ray of
light may be achieved by letting the ray fall on a
surface of a transparent medium in such a way that the
refracted ray makes an angle of 90° with the reflected
ray. The law is named after a Scottish physicist, Sir
David Brewster, who first proposed it in 1811.

3. The figure above shows a ray of ordinary (nonpolarized) light of a given wavelength incident
on a reflecting surface of a transparent medium.

4. • In 1808,Malus discovered that when unpolarised light is reflected from the surface of a
transparent material, the reflected light becomes partially plane-polarised.
• The degree of Polarization depends upon the angle of incidence.
• For a particular angle of incidence, the reflected light is completely plane-polarised with
vibrations perpendicular to the plane of incidence. The angle of incidence is called the
‘Polarising angle’ ip​.
n=tan ip
 This relation is called ‘Brewster’s Law’ and the polarising angle ip is called as ‘Brewster’s angle’.
 A direct conclusion from Brewster’s law is that when light is incident on a transparent surface at the
polarising angle, the reflected and the reflected rays are perpendicular to each other.

5. This can be proved as below:
In figure, PB and PC are the reflected rays
respectively, ip is the angle of incidence and r is the
angle of refraction.
tan ( ' )
tan
Cos
Cos Sin Cos(90 )
90
90 180
18
'
0
p
p
p
p p
Sinr
Sinip
But n i Brewter s Law
Sinip Sinip
i
ip Sinr
or ip r r
i r
i r
C
By
and i r B
Snell sla
PC
BP
w


 



 
  
 

 
  
  
     
 
Thus, reflected ray and refracted ray are mutually perpendicular.

6. The End.
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