Tag: optics

Questions Related to optics

Light from sodium lamp is made to pass through two polaroids placed one after the other in the path of light. Taking the intensity of the incident light as 100%, the intensity of the out coming light that can be varied in the range: 

polarisation of light polarisation wave optics optics physics

  1. 0% to l00%

  2. 0% to 50%

  3. 0% to 25%

  4. 0% to 75%

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Correct Option: B
Explanation:

Let $I _0$ be the intensity of incident light. As the light coming from sodium lamp is unpolarised, so the intensity of the light emerging from the first polaroid is
$I _1 \, = \, \dfrac{I _0}{2}$
If $\theta$ is angle between two polaroids, then the intensity of the light emerging from the second polaroid is
$I _2 \, = \, I _1 \, cos^2\theta \, = \, \dfrac{I _0}{2} cos^2\theta$
But $I _0 \, = \, 100%$ (Given)
$\therefore \, I _1\, = \, 50% \, cos^2\theta$
Since $\theta$ varies from 90 to 0, so the intensity of the outcoming light  can be varied from 0% to 50%.

If the critical angle be $ \theta$ , then the Brewster's angle is

polarisation of light polarisation wave optics optics physics

  1. $\sin^{-1}[\cot \theta]$

  2. $90-\theta$

  3. $\tan^{-1}[cosec \theta]$

  4. $\sin^{-1}[\tan \theta]$

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Correct Option: C

Unpolarised light of intensity $I _{o}$ passes through two polaroids; the axes of one is vertical. The intensity of transmitted light is:

polarisation of light polarisation wave optics optics physics

  1. $\dfrac {l _{0}}{4}$

  2. $\dfrac {l _{0}}{8}$

  3. $\dfrac {l _{0}}{2}$

  4. $\dfrac {3l _{0}}{4}$

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Correct Option: C

The plane of variation and the plane of polarisation of beam of light

polarisation of light polarisation wave optics optics physics

  1. are identical to each other

  2. are orthogonal to each other

  3. make an angle. which depends on the colour of the light

  4. rotate with respect to each other along the path of the beam

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Correct Option: A

Unpolarised light is incident on a glass surface at polarising angle of $57.5^0$, then the angl between the incident ray & refracted ray is :-

polarisation of light polarisation wave optics optics physics

  1. $57.5^0$

  2. $115^0$

  3. $205^0$

  4. $145^0$

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Correct Option: C

Choose the correct statement ______

polarisation of light polarisation wave optics optics physics

  1. Brewster's angle is independent of the wavelength of light.

  2. Brewster's angle is independent of nature of reflecting the surface.

  3. Brewster's angle is different for different wavelengths.

  4. Brewster's angle depends on the wavelength but not on the nature of reflecting the surface.

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Correct Option: C
Explanation:

Brewester's angle depends on the wavelength of light because Brewester's angle depends on the refractive index of medium and refractive index depends on the wavelength of light. 

For a given medium, the polarising angle is $  60^{\circ} .  $ What is the critical angle for this medium?

polarisation of light polarisation wave optics optics physics

  1. $\tan^{-1}(\dfrac 1{\sqrt 3})$

  2. $\sin^{-1}(\dfrac 1{\sqrt 3})$

  3. $\tan^{-1}( {\sqrt 3})$

  4. $\sin^{-1}({\sqrt 3})$

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Correct Option: B

Which of the following properties shows that light is a transverse wave?

polarisation of light polarisation wave optics optics physics

  1. Reflection

  2. Interference

  3. Diffraction

  4. Polarization

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Correct Option: D
Explanation:

The polarization phenomenon, verifies the transverse nature of light. Since sound has longitudinal nature, so it does not show polarization effect.

When the light is incident at the polarizing angle on transparent medium, then the completely polarized light is 

polarisation of light polarisation wave optics optics physics

  1. refracted light

  2. reflected light

  3. refracted and reflected light

  4. neither reflected nor refracted light

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Correct Option: B
Explanation:

When the light is incident at the polarising angle on the transparent medium, the reflected light is completely polarised.

Which of the following cannot be polarised ?

polarisation of light polarisation wave optics optics physics

  1. Radio waves

  2. $\beta$ rays

  3. Infrared rays

  4. $\gamma$ rays

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Correct Option: B
Explanation:

$ \beta $ are stream of particles comprising of electrons moving with very high velocity, hence it cannot be polarized, while others can as they are electromagnetic waves.