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Multiple choice polarisation of light polarisation wave optics optics physics

Which of these waves can be polarised ?

  1. Sound waves

  2. Longitudinal waves on a string

  3. Transverse waves on a string

  4. Light waves
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
  • Only transverse waves can be polarised. Longitudinal waves (sound waves in air) cannot be polarised. The reason that only transverse wave can be polarised is that their vibrations can  be potentially occur in all directions perpendicular to the direction of travel.
  • Polarisation of "light wave" is possible only because they can oscillate in more than one orientation because they are transverse in Nature.
  • It has no dependence  on wavelength and frequencies
  • Hence option D is the right answer
Multiple choice polarisation of light polarisation wave optics optics physics

When unpolarised light is incident on a plane glass plate at Brewster's angle, then which of the following statements is correct?

  1. Reflected and refracted rays are completely polarised with their planes of polarisation parallel to each other

  2. Reflected and refracted rays are completely polarised with their planes of polarisation perpendicular to each other

  3. Reflected light is plane polarised but transmitted light is partially polarised

  4. Reflected light is partially polarised but refracted light is plane polarised
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

At Brewster angle, only the reflected light is completely plane polarised, but the transmitted (refracted) light is partially polarised.

Multiple choice polarisation of light polarisation wave optics optics physics

If the light is polarised by reflection, then the angle between reflected and refracted light is

  1. 180$^o$

  2. 90$^o$

  3. 45$^o$

  4. 36$^o$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When the reflected light is completely polarised, then the angle between reflected and refracted ray are $ { 90 }^{ o }$

Multiple choice polarisation of light polarisation wave optics optics physics

A ray of light strikes a glass plate at an angle of 60$^{o}$. If the reflected and refracted rays are perpendicular to each other, the index of refraction of glass is

  1. $\displaystyle\frac{1}{2}$

  2. $\displaystyle\sqrt{\frac{3}{2}}$

  3. $\displaystyle\frac{3}{2}$

  4. 1.732
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

As reflected and refracted rays are perpendicular to each other, therefore, i$ _p$ = i = 60$^{o}$, where i$ _p$ is called angle of polarisation.
$\displaystyle\mu = tan i _{p} = tan 60^{o} = \sqrt{3}$ = 1.732.

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
$p=tan^{-1}(\dfrac{1}{sin 45^{0}})$
$=tan^{-1}(\dfrac{1}{1/\sqrt{2}})     (\because sin 45^{0}=\sqrt{2})$
$=tan^{-1}(\sqrt{2})$