Q 1 :    

The intensity of transmitted light when a polaroid sheet, placed between two crossed polaroids at 22.5° from the polarization axis of one of the polaroid, is (I0 is the intensity of polarised light after passing through the first polaroid)             [2025]
 

  • I08

     

  • I016

     

  • I02

     

  • I04

     

(1)

[IMAGE 289]

According to the Malus law,

      I=I0cos2(θ1)

      I1=I0                                                      (given)

      I2=I1cos2(θ2)

      I2=I0cos2(22.5)

      I2=I0(0.85)

      I3=I2cos2(θ3)=I0×0.85×cos2(67.5°)

      I3=I0×0.125

or   I3=I08



Q 2 :    

An unpolarized light beam travelling in air is incident on a medium of refractive index 1.73 at Brewster’s angle. Then          [2025]

  • both reflected and transmitted light are perfectly polarized with angles of reflection and refraction close to 60° and 30°, respectively.

     

  • transmitted light is completely polarized with angle of refraction close to 30°

     

  • reflected light is completely polarized and the angle of reflection is close to 60°

     

  • reflected light is partially polarized and the angle of reflection is close to 30°

     

(3)

Brewster's angle, tanθB=μ2μ1

where μ1 is the refractive index of air and μ2 is the refractive index of the given medium, μ2=1.73.

  θB=tan-1(1.73)60°

By law of reflection,

ip=r=60°

When an unpolarised light is incident on a medium of reflective index 1.73 at Brewster’s angle, then reflected light is completely polarised.



Q 3 :    

A beam of unpolarised light of intensity I0 is passed through a polaroid A, then through another polaroid B, oriented at 60° and finally through another polaroid C, oriented at 45° relative to B as shown. The intensity of emergent light is             [2024]

[IMAGE 290]

  • I016

     

  • I04

     

  • I02

     

  • I032

     

(1)

Unpolarised light when passed through a polaroid is reduced to half of its initial value.

So, I1=I02

Using Malus law for polaroid B

       I2=I1cos2θ

I2=I1cos260°

I2=I1(12)2=I14=I08    (cos60°=12)

At polaroid C, I3=I2cos245°

I3=I2(12)2=I22=I016



Q 4 :    

An unpolarised light beam strikes a glass surface at Brewster’s angle. Then                [2024]

  • the reflected light will be partially polarised.

     

  • the refracted light will be completely polarised.

     

  • both the reflected and refracted light will be completely polarised.

     

  • the reflected light will be completely polarised but the refracted light will be partially polarised.

     

(4)

According to Brewster’s law, when an unpolarised light beam strikes a glass surface at Brewster’s angle, then the reflected light is completely polarised and the refracted light will be partially polarised.

 



Q 5 :    

The Brewster's angle ib for an interface should be              [2020]

  • 0°<ib<30°

     

  • 30°<ib<45°

     

  • 45°<ib<90°

     

  • ib=90°

     

(3)

We know, μ=tanib

As 1<μ<     1<tanib<

tan(45°)<tanib<tan(90°)  or  45°<ib<90°



Q 6 :    

Unpolarised light is incident from air on a plane surface of a material of refractive index μ. At a particular angle of incidence i, it is found that the reflected and refracted rays are perpendicular to each other. Which of the following options is correct for this situation?             [2018]
 

  • Reflected light is polarised with its electric vector parallel to the plane of incidence.

     

  • Reflected light is polarised with its electric vector perpendicular to the plane of incidence.

     

  • i=sin-1(1μ)

     

  • i=tan-1(1μ)

     

(2)

[IMAGE 291]

When reflected light and refracted light are perpendicular, reflected light is polarised with electric field vector perpendicular to the plane of incidence.

Also, tani=μ  (Brewster angle)



Q 7 :    

Two polaroids P1 and P2 are placed with their axis perpendicular to each other. Unpolarised light I0 is incident on P1. A third polaroid P3 is kept in between P1 and P2 such that its axis makes an angle 45° with that of P1. The intensity of transmitted light through P2 is         [2017]
 

  • I04

     

  • I08

     

  • I016

     

  • I02

     

(2)

The intensity of transmitted light through P1,

     I1=I02

The intensity of transmitted light through P3,

        I2=I1cos245°=I02(12)2=I02·12=I04

Angle between polaroids P3 and P2=(90°-45°)=45°

  Intensity of transmitted light through P2,

        I3=I2cos245°=I04(12)2=I08