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CSE 1-1 > Optics > Flashcards

Optics Flashcards

1
Q

What is Light?

A

Light is a form of energy which after entering in our eyes gives us the sensation of sight and helps us to see various objects.

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2
Q

Explain Newton’s Corpuscular Theory of Light.

A

Every source of light emits large number of tiny particles known as corpuscles in a medium surrounding the source.

These particles are perfectly elastic, rigid and weightless.

Different colours of light are due to different sizes of these corpuscles.

The weight of the corpuscular being is very small, they are not affected by gravitational force of attraction. Hence they always travel in a straight line.

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3
Q

How Newton explained the reflection and refraction of light?

A

Newton proposed particles of light are repelled by reflecting surface while to explain refraction Newton proposed
that particles of light are attracted by refracting.

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4
Q

What are the drawbacks of Newtons theory?

A

Newton’s theory was unable to explain the partial reflection &
refraction of light at the surface of transparent medium.

Corpuscular theory was unable to explain many phenomena in
light like double refraction, interference, polarization,
diffraction etc.

Corpuscular theory predicted that speed of light in rarer
medium is smaller than speed of light in denser medium. This
was experimentally proved wrong by Foucault.

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5
Q

Explain Huygens wave theory of light.

A

It states that every point on a
wavefront is itself the source of
spherical wavelets, and the
secondary wavelets emanating
from different points mutually
interfere. The sum of these
spherical wavelets forms the
wavefront.

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6
Q

What are the advantages of Hugenes’ Wave Theory of Light?

A

Phenomena like interference, laws of refraction, Reflection,
Simultaneous refraction and reflection, Double Refraction can be explained on the basis of this theory.

According to Huygens, theory the velocity of light in denser medium is less than velocity of light in a rarer medium as was experimentally proved by Focault.

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7
Q

What are the limitations of Hugenes’ Wave Theory of Light?

A

It could not explain phenomenon of polarisation of light and phenomenon like Compton Effect, photoelectric effect.

 Michelson and Morley experiment concluded that there is no ether drag when earth moves through it. This proves ether doesn’t exist. All
the other attempts / experiments to detect Luminiferous ether failed,
which proves that luminiferous ether does not exist.

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8
Q

What was Faradays proposal?

A

Faraday proposed in 1847 that light was a high-frequency
electromagnetic vibration, which could propagate even in the absence of a medium.

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9
Q

What is Maxwells contribution in the electro-magnetic theory of light?

A

He published A Book
on Electricity and Magnetism, which contained a full mathematical
description of the behavior of electric and magnetic fields, still known
as Maxwell’s equations.

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10
Q

Who confirmed Maxwells theory practically?

A

Heinrich Hertz confirmed Maxwell’s theory experimentally by generating and detecting radio waves in the
laboratory and demonstrating
that these waves behaved
exactly like visible light,
exhibiting properties such as
reflection, refraction, diffraction
and interference.

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11
Q

What is wave surface?

A

If point sources emits light waves with velocity c in a
medium , these waves will reach distance ct in time t. If we draw a sphere with center c and radius ct, it is called as spherical wave surface.

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12
Q

What is wavefront?

A

It is defined as the locus of all the points of the medium to
which waves reach simultaneously, so that all the points are in same phase.

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13
Q

What is wave normal?

A

Perpendicular drawn to surface of wave front at any point
in direction of propagation of light is called as wave normal.

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14
Q

What is interference?

A

The phenomenon of redistribution of energy due to super position of light waves from two coherent sources is called interference.

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15
Q

What are the necessary conditions for interference?

A

The sources must be monochromatic.

Two coherent sources are required.

There must be a phase difference or path difference between the two waves.

The amplitude of the waves must be same.

The distance between the two coherent sources of light must be small as possible.

The two waves must travel with the same velocity.

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16
Q

What is the prominent example of interference in nature?

A

A blue morpho butterfly is one of the prominent examples of interference of light in real life. When the light falls on the surface of the wings, the blue colour out of the spectrum
undergoes a constructive interference and the rest colours tend to encounter destructive interference. This is the reason why only a vibrant blue colour is
visible on the surface of the wings.

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17
Q

What natural phenomena of light is seen on soap bubble?

A

Interference of light.

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18
Q

What is constructive interference?

A

In constructive interference the
amplitude of the resultant wave is greater than that of either
individual wave.

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19
Q

What is destructive interference?

A

In destructive interference the
amplitude of the resultant wave is less that that of either
individual wave.

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20
Q

What is Young’s Experiment.

A

In 1801, Young devised and performed an experiment to measure the wavelength of light. Thomas Young recognized that if light behaved like a wave, it would be possible to create patterns of constructive and destructive interference using light. He devised an experiment that would force two beams
of light to travel different distances before interfering with each other when
they reached a screen.

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21
Q

Mathematically prove Young’s experiment.

A

Lecture slide-1 (14-16).

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22
Q

What is Newtons ring?

A

Newton’s ring is a noteworthy illustration of the interference of light that occur between light waves reflected at the
upper and lower surfaces of the air film separating the lens and the flat surface.

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23
Q

Formation of Newton’s ring by reflected light

A

Lecture slide-2 (3-6)

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24
Q

Formation of Newton’s ring by transmitted light

A

Lecture slide-2 (6)

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25
Q

What is diffraction of light?

A

Diffraction refers to a phenomenon that occurs when a wave encounters
an obstacle or opening. It is defined as the bending of waves around the corners of an obstacle or through an aperture. The diffracting object or
aperture effectively becomes a secondary source of the propagating
wave. It occurs when the size of the aperture or obstacle is of
the same order of magnitude as the wavelength of the incident wave.

26
Q

What happens when an aperture width is smaller than the wavelength?

A

In an aperture with width smaller than the wavelength, the wave
transmitted through the aperture spreads all the way round and behaves
like a point source of waves

27
Q

What happens when the slit length is larger than the wavelength?

A

The diffraction pattern made by waves passing through a slit of width a
(larger than λ) can be understood by imagining a series of point sources all
in phase along the width of the slit. The waves moving directly forward are
all in phase (they have zero path difference), so they form a large central
maximum.

28
Q

What If the wave travels at an angle θ from the normal to the slit?

A

then there is a
path difference x between the waves produced at the two ends of the slit.

If the path difference between the top and middle waves is λ/2, then they
are exactly out of phase and cancel each other out. at this angle, so there is
no resultant wave at this angle. Thus, a minimum in the diffraction pattern
is obtained. Diffraction gratings are formed by large numbers of equally
spaced slits or lines that diffract the light falling on them.

29
Q

What is X-ray diffraction?

A

When X-rays pass through a crystal, the crystal behaves like a
diffraction grating, causing x-ray diffraction. Figure below illustrates this phenomenon.

30
Q

Distinguish between interference and diffraction

A

Lecture slide-3 (7)

31
Q

What is Fraunhoffer diffraction?

A

which occurs when the waves incident on the slit and the screen (detector) are plane waves. This diffraction is
produced when both the light source and screen are effectively at an infinite distance from the given obstacle.

32
Q

What is Fresnel diffraction?

A

Fresnel diffraction is the
second type and refers to diffraction produced when either the source
or screen or both are at finite distances from the obstacle.

33
Q

Difference between Fraunhoffer and Fresnel diffraction?

A

Lecture slide-3 (9)

34
Q

What is unpolarized light?

A

Most sources of electromagnetic radiation contain a large number
of atoms or molecules that emit light. The orientation of the
electric fields produced by these emitters may not be correlated,
in which case the light is said to be unpolarized.

35
Q

What are the application of polarization?

A

Polarization is used in sunglasses to reduce the glare.

Polaroid filters are used in plastic industries for performing stress analysis
tests.

Three-dimensional movies are produced and shown with the help of
polarization.

Polarization is used for differentiating between transverse and longitudinal
waves.

Infrared spectroscopy uses polarization.

It is used in seismology to study earthquakes.

In Chemistry, the chirality of organic compounds is tested using polarization
techniques.

36
Q

What is polarization of light?

A

The process of confining the vibrations of the electric vector of light waves to one direction is called polarization of light.

37
Q

What is plane of vibration?

A

A plane including the direction of light propagation and the
direction of electric field.

38
Q

What is plane of polarization?

A

The plane perpendicular to the plane of vibration.

39
Q

What are the methods used in polarization of light?

A

(i) Polarization by Transmission

(ii) Polarization by Reflection

(iii) Polarization by Scattering

(iv) Polarization by Refraction

40
Q

What is linear polarization?

A

In linear polarization, the electric field of light is limited to a single plane along the direction of propagation.

41
Q

What is Circular Polarization?

A

There are two linear components in the electric field of light that are
perpendicular to each other such that their amplitudes are equal, but the phase
difference is π/2. The propagation of the occurring electric field will be in a
circular motion.

42
Q

What is elliptical polarization?

A

The electric field of light follows an elliptical propagation. The amplitude and phase difference between the two linear components are not equal.

43
Q

What is double refraction?

A

Double refraction is the decomposition of a ray of
light into two rays when it passes through certain anisotropic materials, such as calcite crystals.

44
Q

What is optical axis?

A

The structure of the material
with uniaxial anisotropy is such that it has an axis of symmetry
which is known as the optical axis (line passing through the
optical centre and centre of curvature)

45
Q

What is extraordinary and ordinary light?

A

Light with linear polarizations parallel and perpendicular to optical axis has unequal indices of refraction, denoted ne and no respectively, where the suffixes stand for extraordinary and ordinary. Along the optic axis the O-ray and E-ray travel with the same speed.

46
Q

Example of some uniaxial crystals are?

A

calcite, quartz and tourmaline

47
Q

What is birefringence?

A

mica and
selenite have two optic axis, they are biaxial crystals. The phenomenon
is also known as birefringence.

48
Q

What is negative crystal?

A

Negative crystals are crystals in which refractive index corresponding
to E-Ray (𝑛𝐸) is less than the refractive index corresponding to O-Ray
(𝑛o) in all directions except for Optic axis. The E-Ray travels faster
than O-Ray except along the Optic axis. The spherical O-Wavefront is
entirely within the ellipsoidal E -Wavefront. Ex: Calcite, Tourmaline,
Ruby.

49
Q

What is positive crystal?

A

Positive crystals are crystals in which refractive for O-Ray is less than
that for E-Ray (𝑛o < 𝑛𝐸). The velocity of O-Ray is greater than or
equal to the velocity of E-Ray. The ellipsoidal E-wavefront is entirely
within the spherical O-wavefront. Example : Quartz (SiO2), Sellaite
(MgF2), Rutile (TiO2).

50
Q

What is optic indicatrix?

A

As the refractive index varies with the direction of vibration of the light waves for
most crystals, it is of great assistance to visualise the values of “n” for all the
directions of vibration and relate them to the directions of propagation, which will
be perpendicular. The geometric figure which results is called the optic indicatrix.

For some minerals, the optic indicatrix is a sphere. This is the case of those that
are isotropic.

51
Q

What is uniaxial crystal?

A

Uniaxial crystal: A crystal which has only one optic axis is called uniaxial
crystal. It belongs to the tetragonal or hexagonal crystal systems. it is an
ellipsoid of revolution (with two principle axes).

52
Q

What is biaxial crystal?

A

A crystal which has only two optic axis is called biaxial crystal.
It belongs to the orthorhombic, monoclinic, or triclinic crystal. It is an ellipsoid with three principle axes

53
Q

What is Brewster’s Law?

A

In 1811, Brewster found that ordinary light is completely polarized in the
plane of incidence when it gets reflected from a transparent medium at a
particular angle known as the angle of polarization. He was also able to prove
that the tangent of the angle of polarization is numerically equal to the
refractive index of the medium. Moreover, the reflected and refracted rays are
perpendicular to each other.

54
Q

Prove brewsters law mathmatically.

A

Slide-4 page-17

55
Q

What is malus law?

A

According to malus, when completely plane polarized light is incident
on the analyzer, the intensity I of the light transmitted by the analyzer is
directly proportional to the square of the cosine of angle between the
transmission axes of the analyzer and the polarizer.

56
Q

Prove malus law mathematically?

A

Slide-4 page-19

57
Q

What is waveplate?

A

Waveplates (retardation plates or
phase shifters) are made from
materials which exhibit
birefringence. It is an optical device
that alters the polarization state of a
light wave travelling through it.

58
Q

What is full waveplate?

A

When the thickness of crystal is such that path
difference between E-ray and O-ray is λ or phase difference is 2π
then wave plate is known as full wave plate.

59
Q

What is half wave-plate?

A

When the thickness of crystal is such that path difference
between E-ray and O-ray is λ/2 or phase difference is π then wave plate is
known as half wave plate.

60
Q

What is quarter wave-plate?

A

When the thickness of crystal is such that path
difference between E-ray and O-ray is λ/4 or phase difference is π/2 then
wave plate is known as quarter wave plate. A quarter-waveplate can also be
used to create plane-polarization from circular polarization

61
Q

Write down the equation of t for full, half and quarter waveplate?

A

slide-4.

CSE 1-1 (4 decks)

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