Tag: polarisation

Questions Related to polarisation

Polarising angle for water is ${ 53 }^{ o }{ 4 }^{ \prime  }$. If light is incident at this angle on water and reflected, the angle of refraction is :

polarisation of light polarisation wave optics optics physics

  1. ${ 126 }^{ o }{ 56 }^{ \prime }$

  2. ${ 36 }^{ o }{ 56 }^{ \prime }$

  3. ${ 30 }^{ o }$

  4. ${ 36 }^{ o }{ 20 }^{ \prime }$

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Correct Option: B
Explanation:

Polarising angle for water, $i _p = 53^o4'$

Angle of refraction, $r = 90^o - i _p$
$\Rightarrow $  $r = 90^o - 53^o 4'$
$\Rightarrow r = 89^o 60' - 53^o 4'  = 36^o 56'$

A plane polarized light passed through successive polarizers which are rotated by $30^{\circ}$ with respect to each other in the clockwise direction. Neglecting absorption by the polarizers and given that the first polarizer's axis is parallel to the plane of polarization of the incident light, the intensity of light at the exit of the fifth polarizer is closest to.

polarisation of light polarisation wave optics optics physics

  1. Same as that of the incident light

  2. $17.5$% of the incident light

  3. $30$% of the incident light

  4. Zero

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Correct Option: C
Explanation:

$I=I _o (cos^2\phi)^4$

$I=I _o (cos^230)^4$
$I=30$% of $I _o$

The refractive index of the medium, for the polarising angle $60^o$ is?

polarisation of light polarisation wave optics optics physics

  1. $1.732$

  2. $1.414$

  3. $1.5$

  4. $1.468$

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Correct Option: A
Explanation:

Relation between refractive index of medium and polarising angle is given by
$n = \tan i _p$
Given :  Polarising angle  $i _p = 60^o$
So, refractive inedx  $n = \tan (60^o) = 1.732$

When the separation between the central maxima of the two objects is greater than a separation between central maximum of a first object and the first minima of the first object, then objects are said to be

polarisation of light polarisation wave optics optics physics

  1. just resolved

  2. well resolved

  3. not resolved

  4. none of the above

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Correct Option: B
Explanation:

well resolved (definition of qualia)

The diameter of an objective of a telescope, which can just resolve two stars situated at an angular displacement of ${10^{ - 4}}$ degree, should be $\left( {\lambda  = 5000\,{A^0}} \right)$ 

polarisation of light polarisation wave optics optics physics

  1. 35 mm

  2. 35 cm

  3. 35 m

  4. None of the above

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Correct Option: B
Explanation:

$\Delta \theta  = \left( {\dfrac{{1.22\lambda }}{d}} \right)$
$d = \left( {\dfrac{{1.22 \times \lambda }}{{\Delta \theta }}} \right)$
$ \Rightarrow \,\,{10^{ - 4}}\, \to \,\dfrac{\lambda }{{180}} \times {10^{ - 4}}$
$ = 1.74 \times {10^{ - 6}}\,rad.$
$d = \left( {\dfrac{{1.22 \times 5000 \times {{10}^{ - 10}}}}{{1.74 \times {{10}^{ - 6}}}}} \right)$
$ = 0.35\,m\,\,or\,\,35\,cm$

A beam of natural light falls on a system of 5 polaroids, which are arranged in succession such that the pass axis of each Polaroid is turned through $60^0$ with respect to the preceding one. The fraction of the incident light intensity that passes through the system is

polarisation of light polarisation wave optics optics physics

  1. $\dfrac{1}{64}$

  2. $\dfrac{1}{32}$

  3. $\dfrac{1}{256}$

  4. $\dfrac{1}{128}$

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Correct Option: C

What proves that light is a transverse wave?

polarisation of light polarisation wave optics optics physics

  1. Polarization

  2. Reflection

  3. Refraction

  4. Interference

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Correct Option: A
Explanation:

A transverse wave is a wave that oscillates perpendicular to its direction of propagation.  Polarization of light proved that light is a transverse wave.

The helical structures of nucleic acids can be studied by using :

polarisation of light polarisation wave optics optics physics

  1. Interference phenomenon

  2. Diffraction pattern

  3. Polarised light

  4. Photoelectric effect

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Correct Option: C
Explanation:

Polarised light is used to studied helical structures of nucleic acids using different methods such as optical rotatory dispersion. In this method due to refractive indices of the medium for left and right circularly polarised light reflects the structural details of such molecular complexes.

In the light emerging from calcite crystal :

polarisation of light polarisation wave optics optics physics

  1. Both O-ray and E-ray are partially polarised

  2. Both O-ray and E-ray are completely polarised

  3. O-ray is partially polarised and E-ray is completely polarised.

  4. O-ray is completely polarised and E-ray is partially polarised.

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Correct Option: B
Explanation:

Because of birefringence the ordinary and extra ordinary ray are completely polarized.

In double refraction :

polarisation of light polarisation wave optics optics physics

  1. the velocity of the E-ray varies with direction

  2. e-ray does not obey Snell's law

  3. $\mu $ of E-ray is constant

  4. both A and B

Show answer
Correct Option: D
Explanation:

Because the speed of light waves in a medium is equal to their speed in a vacuum divided by the index of refraction for that wavelength, an extra ordinary ray can be either faster or slower than an ordinary ray. The extra ordinary ray does not obey snell's law. It is because refractive index of the e-ray varies according to the direction taken because it has components that are both parallel and perpendicular to the crystal's optic axis.