A plane-polarised light beam of intensity 50 Wm^-2 falls on a smooth air-glass i
ID: 584453 • Letter: A
Question
A plane-polarised light beam of intensity 50 Wm^-2 falls on a smooth air-glass interface at an angle of incidence of 75degree. The incoming light is polarised at 45degree to the plane of incidence and the refractive index of the glass is n_g = 1.71. (i) Determine the angles of reflection and refraction of the beam at the interface. Next, determine (ii) the polarisation and intensity of the reflected beam, and (iii) the polarisation and intensity of the transmitted beam. Quote your polarisation angles relative to the plane of incidence, (iv) Finally, compute the value of n_g which for this configuration would produce reflected light with a polarisation perpendicular to the plane of incidence.Explanation / Answer
(1) reflection angle:
According to The law of reflection, the relationship between the incident angle and the reflected angle for a ray of light incident on a surface. The angles are measured relative to the surface normal (a line that is perpendicular to the surface), not relative to the surface itself. Here's the formula:
i = r
the given value of incident angle is (i) = 75 degrees, so angle of reflection is (r) is 75 degrees.
(2) angle of refraction:
According to Snell's law:
n1 sin 1 = n2 sin 2
n1 is the refractive index of air (value is 1), 1 is reflected angle
n2 is the refractive index of glass, 2 is the refrcated angle
Sin 750 = 1.52 × Sin 2
Sin-1 (0.965 /1.52) = 2
so refractive angle is 400
We know angle of incidence(i) = 750 ; angle of transmission is (t) =400
Fresnel's euations for reflection co.efficients:
= -0.327
= -0.632
The transmission coefficients are:
= 0.449
= 0.368
The signs of the coefficients depends on the original choices of field diretions.
If the angle of incidence is Brewster's angle, then any reflected light will be polarized perpendicularly to the plane of incidence. If the incident light happens to be polarized in the plane of incidence, then no light will be reflected.
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