Tag: polarisation

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Questions Related to polarisation

Multiple choice polarisation of light polarisation wave optics optics physics

A parallel beam of monochromatic unpolarised light is incident on a transparent dielectric plate of refractive index $\displaystyle\frac{1}{\sqrt{3}}$. The reflected beam is completely polarised. Then the angle of incidence is

  1. 30$^{o}$
  2. 60$^{o}$
  3. 45$^{o}$
  4. 75$^{o}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Using Brewster law, $ \tan { { i } _{ p } } =\mu$

$ \Rightarrow { i } _{ p }=\tan ^{ -1 }{ \mu  } $
$=\tan ^{ -1 }{ \left( \dfrac { 1 }{ \sqrt { 3 }  }  \right)  } $
$={ 30 }^{ o }$

Multiple choice polarisation of light polarisation wave optics optics physics

Which of the following phenomena can be demonstrated by light. But not with sound waves in an air column ?

  1. Reflection

  2. Diffraction

  3. Refraction

  4. Polarization
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

To have polarized waves, they first need to be transverse waves - the disturbance needs to be at right angles to the direction of propagation. Therefore sound waves in air (the usual sort) or in other gases and liquids can't be polarized because they're purely compressive.
Hence, option D is correct.

Multiple choice polarisation of light polarisation wave optics optics physics

If the incident light is linearly polarised, then the directional distribution of emitted electrons will peak in the direction of

  1. polarisation

  2. electric field

  3. magnetic field

  4. both (a) and (b)
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
If the incident light is linearly polarized then the directional distribution of emitted electrons will peak in the direction of polarization (the direction of the electric field).
Multiple choice polarisation of light polarisation wave optics optics physics

Assertion: Radio waves can'be polarised.
Reason: Sound waves in air are longitudinal in nature.

  1. If both assertion and reason are true but the reason is the correct explanation of assertion

  2. If both assertion and reason are true but the reason is not the correct explanation of assertion

  3. If assertion is true but reason is false

  4. If both the assertion and reason are false

  5. If reason is true but assertion is false
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Radio waves can be polarized because they are transverse in nature.
And Sound waves in air are longitudinal in nature.
Multiple choice polarisation of light polarisation wave optics optics physics

A parallel beam of natural light is incident at an angle of 58$^{\circ}$ on a plane glass surface. The reflected beam is completely linearly polarized(tan 58$^{\circ}=$1.6). The angle of refraction of the transmitted beam and the refractive index of the glass are :

  1. 32$^{\circ}$, 1.6
  2. 3.2$^{\circ}$, 1.6
  3. 32$^{\circ}$, 1.3
  4. 3.2$^{\circ}$, 1.3
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

If the light in incident on the surface with an
angle of incidence i given by tan i $=\mu $,
the reflected light is completely polarized.
Thus $\mu =tan 58^{0}$
refractive $\mu =1.6$
index
From snell's law
$\dfrac{sin i}{sin \gamma }=\mu $
$\dfrac{sin 58^{0}}{1.6}=sin \gamma $
$\gamma =32^{0}$

Multiple choice polarisation of light polarisation wave optics optics physics

If the critical angle of a crystal is $45^{\circ}$, the polarizing angle is :

  1. $\tan^{-1}\sqrt{2}$
  2. $\tan^{-1}\sqrt{\dfrac{1}{\sqrt{2}}}$
  3. $45^{\circ}$
  4. $37^{\circ}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$tan  p =\dfrac{1}{sinc}$
where p is polarising angle
c is critical angle
$p=tan^{-1}(\dfrac{1}{sin 45^{0}})$
$=tan^{-1}(\dfrac{1}{1/\sqrt{2}})     (\because sin 45^{0}=\sqrt{2})$
$=tan^{-1}(\sqrt{2})$

Multiple choice polarisation of light polarisation wave optics optics physics

When an unpolarized light of intensity ${I} _{0}$ is incident on a polarizing sheet, the intensity of the light which does not get transmitted is:

  1. $\dfrac{1}{2} {I} _{0}$
  2. $\dfrac{1}{4} {I} _{0}$

  3. Zero
  4. ${I} _{0}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$I={ I } _{ 0 }\cos ^{ 2 }{ \theta  } $
Intensity of polarized light $=\dfrac { { I } _{ 0 } }{ 2 } $
$\therefore$ Intensity of untransmitted light $={ I } _{ 0 }-\dfrac { { I } _{ 0 } }{ 2 } =\dfrac { { I } _{ 0 } }{ 2 } $

Multiple choice polarisation of light polarisation wave optics optics physics

When the angle of incidence on a material is ${60}^{o}$, the reflected light is completely polarised. The velocity of the refracted ray inside the material is

  1. $3\times {10}^{8}$
  2. $\cfrac{3}{\sqrt {2}}\times {10}^{8}$
  3. $\sqrt {3}\times {10}^{8}$
  4. $0.5\times {10}^{8}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

From Brewster's law
$\mu=\tan{{i} _{p}}$
$\Rightarrow$ $\cfrac{c}{v}=\tan{{60}^{o}}$
$=\sqrt {3}$
$\Rightarrow$ $v=\cfrac{c}{\sqrt{3}}$
$=\cfrac{3\times {10}^{8}}{\sqrt {3}}=\sqrt {3}\times {10}^{8}m/s$

Multiple choice polarisation of light polarisation wave optics optics physics

When unpolarised light beam is incident from air onto glass $(n=1.5)$ at the polarising angle.

  1. Reflected beam is polarised $100$ percent

  2. Reflected and refracted beams are partially polarised

  3. The reason for (a) is that almost all the light is reflected

  4. All of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A

When the incident light crosses the interface the light is absorbed temporarily by the atoms in the second medium. Electrons in these atoms oscillate back any forth in the direction of the electric field vectors in the refracted ray,  perpendicular to the direction,  the refracted ray is travelling. 
The light is remitted by the atoms to form both the reflected and refracted rays. The electric field vector in the light match the directions the electrons were oscillating,  and they must've be perpendicular to the direction of propagation of the wave.  When the lights comes in at the Brewster angle the reflected wave has no electric field vectors parallel to the refracted ray, because the electrons Di not oscillate along that direction. The reflected wave also have no electric field vectors parallel to the reflected ray, because that's the direction of propagation of the wave. The only direction possible is perpendicular to the plane of the picture. So,  the reflected ray is linearly polarized. 

Multiple choice polarisation of light polarisation wave optics optics physics

The solar glare of sunlight bouncing off water or snow can be a real problem for drivers. The reflecting sunlight is horizontally polarized, meaning that the light waves oscillate at an angle of $90^o$ to a normal line drawn perpendicular to the Earth. At what angle relative to this normal line should sunglasses be polarized if they are to be effective against solar glare? 

  1. $0^o$
  2. $30^o$
  3. $45^o$
  4. $60^o$
  5. $90^o$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The idea behind polarized sunglasses is to eliminate the glare. If the solar glare is all at a $90^o$ angle to the normal line, sunglasses polarized at a $ 0^o$ angle to this normal will not allow any of the glare to pass. Most other light is not polarized, so it will still be possible to see the road and other cars, but the distracting glare will cease to be a problem.