Tag: optics

Questions Related to optics

If the polarizing angle for a given medium is $60^{\circ}$, then the refractive index of the medium is 

polarisation of light polarisation wave optics optics physics

  1. $\dfrac{1}{\sqrt 3}$

  2. $\sqrt{\dfrac{3}{2}}$

  3. 2

  4. $\sqrt{3}$

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Correct Option: D

A polarizer and an analyzer are arranged with their optic axes parallel to each other Symmetric light first passes through the polarizer and then the analyzer and the intensity of the light emerging is 'I'. If the analyzer is turned through $30^o$, the percent changes in the intensity is

polarisation of light polarisation wave optics optics physics

  1. $75\%$

  2. $50\%$

  3. $25\%$

  4. $40\%$

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Correct Option: C

When unpolarized light beams are incidents in the air into glass ($n=1.5$ at polarising angle)

polarisation of light polarisation wave optics optics physics

  1. reflected beams is $100$ polarised

  2. reflect and refracted beams are partially polarised

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

  4. all the above

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Correct Option: A
Explanation:

When unpolarized light is incident at Brewster angle from one medium to another, the light that is reflected from the surface is perfectly polarized

Dichorism means

polarisation of light polarisation wave optics optics physics

  1. selective absorption of unpolarised light.

  2. selective absorption of dispersed light.

  3. selective absorption of scattered light.

  4. selective absorption of one of the polarised component.

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Correct Option: D
Explanation:

Dichromism is the selective absorption of one orthogonal polarization component of an incident beam over the other. this phenomenon is due to anisotropy of the material, with one polarization component experiencing preferential absorption.

From Brewster's law, it follows that the angle of polarization depends upon

polarisation of light polarisation wave optics optics physics

  1. the wavelength of light

  2. orientation of the plane of polarization

  3. orientation of the plane of vibration

  4. none of these

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Correct Option: A
Explanation:

$\theta _B=tan^{-1}\dfrac{n _2}{n _1}$

Since the refractive index for a given medium changes depending on the wavelength of light, Brewster's angle will also vary with wavelength.

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

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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

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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

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Correct Option: C
Explanation:

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