Physics · Science General

Optics and Light Properties

2,019 Questions

Optics and light properties focus on the behavior of light, including reflection, refraction, dispersion, and polarization. This topic also covers the wave nature of light, illumination, and the functioning of optical instruments like microscopes. Questions on these concepts are common in general science sections of SSC, Railways, and State exams.

Reflection and mirrorsRefraction and mediumsLight wave theoriesPolarization and intensity

Optics and Light Properties Questions

Multiple choice polarisation of light polarisation wave optics optics physics

The transverse nature of light waves is verified by

  1. reflection of light

  2. polarisation of light

  3. refraction of light

  4. interference of light
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

Multiple choice polarisation of light polarisation wave optics optics physics

$\lambda _a$ 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 

  1. $\lambda _a=\lambda _m\tan 2=\theta$
  2. $\lambda _m=\lambda _a\tan ^2=\theta$
  3. $\lambda _a=\lambda _m\cot=\theta$
  4. $\lambda _m=\lambda _a\cot=\theta$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

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

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

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

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

Multiple choice polarisation of light polarisation wave optics optics physics

When an unpolarized light of intensity ${I} _{0}$ is incident on a polarizing sheet, the intensity of the light which does not get transmitted is:

  1. $\dfrac{1}{2} {I} _{0}$
  2. $\dfrac{1}{4} {I} _{0}$

  3. Zero
  4. ${I} _{0}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$I={ I } _{ 0 }\cos ^{ 2 }{ \theta  } $
Intensity of polarized light $=\dfrac { { I } _{ 0 } }{ 2 } $
$\therefore$ Intensity of untransmitted light $={ I } _{ 0 }-\dfrac { { I } _{ 0 } }{ 2 } =\dfrac { { I } _{ 0 } }{ 2 } $

Multiple choice polarisation of light polarisation wave optics optics physics

When the angle of incidence on a material is ${60}^{o}$, the reflected light is completely polarised. The velocity of the refracted ray inside the material is

  1. $3\times {10}^{8}$
  2. $\cfrac{3}{\sqrt {2}}\times {10}^{8}$
  3. $\sqrt {3}\times {10}^{8}$
  4. $0.5\times {10}^{8}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

From Brewster's law
$\mu=\tan{{i} _{p}}$
$\Rightarrow$ $\cfrac{c}{v}=\tan{{60}^{o}}$
$=\sqrt {3}$
$\Rightarrow$ $v=\cfrac{c}{\sqrt{3}}$
$=\cfrac{3\times {10}^{8}}{\sqrt {3}}=\sqrt {3}\times {10}^{8}m/s$

Multiple choice polarisation of light polarisation wave optics optics physics

When unpolarised light beam is incident from air onto glass $(n=1.5)$ at the polarising angle.

  1. Reflected beam is polarised $100$ percent

  2. Reflected and refracted beams are partially polarised

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

  4. All of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A

When the incident light crosses the interface the light is absorbed temporarily by the atoms in the second medium. Electrons in these atoms oscillate back any forth in the direction of the electric field vectors in the refracted ray,  perpendicular to the direction,  the refracted ray is travelling. 
The light is remitted by the atoms to form both the reflected and refracted rays. The electric field vector in the light match the directions the electrons were oscillating,  and they must've be perpendicular to the direction of propagation of the wave.  When the lights comes in at the Brewster angle the reflected wave has no electric field vectors parallel to the refracted ray, because the electrons Di not oscillate along that direction. The reflected wave also have no electric field vectors parallel to the reflected ray, because that's the direction of propagation of the wave. The only direction possible is perpendicular to the plane of the picture. So,  the reflected ray is linearly polarized. 

Multiple choice polarisation of light polarisation wave optics optics physics

The solar glare of sunlight bouncing off water or snow can be a real problem for drivers. The reflecting sunlight is horizontally polarized, meaning that the light waves oscillate at an angle of $90^o$ to a normal line drawn perpendicular to the Earth. At what angle relative to this normal line should sunglasses be polarized if they are to be effective against solar glare? 

  1. $0^o$
  2. $30^o$
  3. $45^o$
  4. $60^o$
  5. $90^o$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The idea behind polarized sunglasses is to eliminate the glare. If the solar glare is all at a $90^o$ angle to the normal line, sunglasses polarized at a $ 0^o$ angle to this normal will not allow any of the glare to pass. Most other light is not polarized, so it will still be possible to see the road and other cars, but the distracting glare will cease to be a problem. 

Multiple choice polarisation of light polarisation wave optics optics physics

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 :

  1. ${ 126 }^{ o }{ 56 }^{ \prime }$
  2. ${ 36 }^{ o }{ 56 }^{ \prime }$
  3. ${ 30 }^{ o }$
  4. ${ 36 }^{ o }{ 20 }^{ \prime }$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

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

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