Tag: wave optics

Questions Related to wave optics

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

polarisation of light polarisation wave optics optics physics

  1. Reflect and refracted rays are completely polarized with their planes of polarization parallel to each other.

  2. Reflect and refracted rays are completely polarized with their planes of polarization perpendicular to each other.

  3. Reflected light is the plane polarized but transmitted light is partially polarized.

  4. Reflected light is partially polarized but refracted light is plane polarized.

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Correct Option: B
Explanation:

Reflect and refracted rays are completely polarized with their planes of polarization perpendicular to each other.
option $B$ is correct 

The transverse nature of light waves is verified by

polarisation of light polarisation wave optics optics physics

  1. reflection of light

  2. polarisation of light

  3. refraction of light

  4. interference of light

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Correct Option: B
Explanation:

Phenomenon of polarisation helps in establishing the fact that light waves are transverse in nature, otherwise it was believed that they are longitudinal in nature like sound waves.

$\lambda _a$ and $\lambda _m$ are the wavelengths of the beam of light in air and in medium, respectively. If $\theta$ is the polarizing angle then, the correct relationship between $\lambda _a, \lambda _m$ and $\theta$ is 

polarisation of light polarisation wave optics optics physics

  1. $\lambda _a=\lambda _m\tan 2=\theta$

  2. $\lambda _m=\lambda _a\tan ^2=\theta$

  3. $\lambda _a=\lambda _m\cot=\theta$

  4. $\lambda _m=\lambda _a\cot=\theta$

Show answer
Correct Option: D
Explanation:

Brewster's angle or polarizing angle is given by $\tan\theta=\dfrac{n _{medium}}{n _{air}}=\dfrac{\lambda _a}{\lambda _m}$

Thus $\lambda _m=\lambda _a\cot\theta$

Which of these waves can be polarised ?

polarisation of light polarisation wave optics optics physics

  1. Sound waves

  2. Longitudinal waves on a string

  3. Transverse waves on a string

  4. Light waves

Show answer
Correct Option: D
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

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

polarisation of light polarisation wave optics optics physics

  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

Show answer
Correct Option: C
Explanation:

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

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

polarisation of light polarisation wave optics optics physics

  1. 180$^o$

  2. 90$^o$

  3. 45$^o$

  4. 36$^o$

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Correct Option: B
Explanation:

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

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

polarisation of light polarisation wave optics optics physics

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

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

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

  4. 1.732

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Correct Option: D
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.

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

polarisation of light polarisation wave optics optics physics

  1. 30$^{o}$

  2. 60$^{o}$

  3. 45$^{o}$

  4. 75$^{o}$

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Correct Option: A
Explanation:

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

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

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

polarisation of light polarisation wave optics optics physics

  1. Reflection

  2. Diffraction

  3. Refraction

  4. Polarization

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Correct Option: D
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.

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

polarisation of light polarisation wave optics optics physics

  1. polarisation

  2. electric field

  3. magnetic field

  4. both (a) and (b)

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Correct Option: D
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).