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Waves And Optics Flashcards

1
Q

What is a wave?

A

Transfer of energy without the transfer of matter

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2
Q

What is a transverse wave?

A

A type of wave where energy moves perpendicular to the oscillations

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3
Q

What is amplitude?

A

The maximum displacement from equilibrium

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4
Q

What is wavelength?

A

The distance from one point on the wave to the next consecutive point that is in phase

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5
Q

What is the time period?

A

The time taken for one whole oscillation

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6
Q

What is frequency?

A

The number of oscillations per second

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7
Q

What is constructive interference?

A

When 2 or more waves have displacement in the same direction

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8
Q

What is destructive interference?

A

When one wave has positive displacement and the other has negative displacement (if they are equal total destructive interference occurs)

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9
Q

What is a node (waves)?

A

Region of no displacement

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10
Q

What is an antinode?

A

Region of maximum displacement

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11
Q

What is the fundamental frequency?

A

The lowest frequency of a stationary wave that can be supported by a system

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12
Q

How do you determine the resultant displacement after interference?

A

The vector sum of displacements?

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13
Q

What is a stationary wave?

A

A wave where energy is not transferred from one point to another, but oscillations still happen.

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14
Q

How far must two points be to support a stationary wave.

A

An integer number of half wave lengths

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15
Q

What are the two ways a station wave can be formed?

A
  • 2 coherent progressive waves travelling in opposite directions.
  • Reflecting a wave of a constant frequency and amplitude between two points.
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16
Q

What are coherent waves?

A

Waves of a fixed phase relationship, same frequency and of the same type.

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17
Q

What is refraction?

A

Change in direction of waves as it travels through different media caused by the medium’s optical density.

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18
Q

What is the refractive index of air?

A

1

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19
Q

What is the refractive index of a material?

A

A measure of how fast light travels through it compared to the speed of light in a vacuum. (c/v)

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20
Q

Why does a perpendicular ray not refract?

A

There is no evidence of a change in the speed or direction.

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21
Q

What is the relationship between frequency and refraction?

A

The higher the frequency the larger the change in wavelength and speed.

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22
Q

What is the critical angle of incidence?

A

One where the angle of refraction is 90 degrees

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23
Q

What are the condition necessary for a critical angle?

A
  1. There must be an increase in angle with the normal
  2. Must be an increase in speed
  3. n1 > n2
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24
Q

What happens if we exceed the critical angle?

A

Total internal reflection

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25
Q

What is the role of the cladding in a fibre optic cable?

A
  • Protect the core from damage and scratching
  • Prevent signal degradation
  • Keeps signal secure
  • Keeps core separate from other fibres preventing information crossover
  • Provides a boundary for TIR
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26
Q

How can we deal with pulse absorption?

A
  • Use repeaters
  • Increase the intensity of the pulse
  • Use a beam that diffracts less
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27
Q

Describe Spectral/Material Dispersion in reference to fibre optics.

A
  • If white light is used each component frequency has a different speed in a medium due to different refractive indexes
  • Violet has the greatest change in speed and red the least
  • Violet travels slower than red
  • A broadened signal is received by the sensor
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28
Q

Describe the results of Pulse Broadening.

A
  • Pulse is wider as the pulse arrives at different times
  • Pulse is a lower intensity as less energy is arriving per second
29
Q

What is the solution to spectral/material dispersion?

A

Use a monochromatic source of light

30
Q

Describe Modal Dispersion

A
  • Each part of the wavefront arrives at different angles of incidence
  • Reflects at a different angle so each takes a different path
  • Path with more internal reflections take longer
  • Pulse broadening is observed
31
Q

How is Modal Dispersion reduced?

A
  • Using a narrow fibre to reduce the number of alternate paths the light can take
  • Increasing core-cladding critical angle to lose rays with a high angle of incidence in the cladding
32
Q

Why do diamonds sparkle?

A
  • High refractive index of 2.4 so separates colours more
  • Gives a small critical angle of 24 degrees
  • Total internal reflections occur many times before rays are transmitted
  • Colours spread out even more and so the diamond sparkles with different colours
33
Q

What are some of the required properties of the core?

A
  • Material should have a low absorption
  • Refractive index should not vary much across the wavelengths of light that are to be used
34
Q

What are some of the properties of the cladding?

A
  • Lower refractive index than the core
  • Has a high enough refractive index so that a sufficient number of high incidence rays are lost in the cladding
35
Q

Why do we want to reduce pulse broadening?

A

Prevent individual pulses in a series from overlapping so that we get a clearer signal

36
Q

What is diffraction?

A

The change in direction of waves when they encounter an obstacle or pass through an aperture

37
Q

What is a diffraction grating?

A

Specially constructed pieces of glass which have many tiny apertures. Grating spacing given in lines per mm.

38
Q

When is the effect or diffraction greatest?

A

When the aperture size is equal to the wavelength

39
Q

When do we get an interference pattern?

A

If two coherent light-waves diffract through two apertures.

40
Q

When asked to describe Young’s slits or a diffraction grating what kind of terms should you use?

A
  • coherent
  • monochromatic
  • wavelength
  • path difference
  • interference
41
Q

How do you describe white light that is shone through a slit?

A
  • Central maximum is white
  • Next fringe is a gradient, from blue to red, inside out
42
Q

What is spectrometry?

A

Light emitted, reflected, or absorbed by a material can give useful information about its structure or composing elements.

43
Q

What is Huygen’s Principle?

A

A wavefront is composed of many small point sources of secondary waves - “wavelets”. The next wavefront is created by the constructive interference of these secondary wavelets.

44
Q

What are the differences between single slit interference and Young’s slits?

A
  • Central maximum is twice as wide as the outer fringes
  • Peak intensity of each fringe decreases with distance from centre
  • Each of the outer fringes are the same width as each other
45
Q

What is incident light?

A

Light that approaches an inter-medium boundary

46
Q

What is light?

A

An electromagnetic wave

47
Q

What is absorption of light?

A

Energy transferred into a store, usually thermal/kinetic energy

48
Q

What are electromagnetic waves composed of?

A

Oscillating electric and magnetic fields. Their oscillations are perpendicular to each other and the direction of travel.

49
Q

What determines the plane of polarisation?

A

The electric field’s plane of oscillation

50
Q

What is a polarising filter?

A

A filter that only transmits one polarisation of light

51
Q

How can we calculate the amplitude of a wave after it has passed through a polarised filter?

A

Find the component of the light wave that is parallel to the direction of polarisation

52
Q

What are the key points to mention when asked a polarisation question?

A
  • Rotation in the vertical plane
  • When vertical signal is a maximum and when horizontal signal is a minimum
  • Maximum occurs when filter is aligned with the polarisation of the wave
53
Q

How can we determine where interference will occur in Young’s slits?

A

We take the max and min angles of rays at each slit and see where they overlap with a path difference of at least one wavelength

54
Q

What can we talk about when considering two points on a stationary wave?

A
  • Fixed phase relationships (mention if it is in phase or not)
  • Amplitudes
  • Frequencies
  • Oscillation speeds
55
Q

What are the requirements for a stationary wave?

A
  • Same wave speed
  • Moving in opposite directions
  • Same wavelength/frequency
56
Q

What equation links period and frequency?

57
Q

What equations links wave speed, frequency and wavelength?

58
Q

What is the distance between adjacent nodes in a stationary wave?

59
Q

How does frequency change as the harmonic increases?

A

The nth harmonic has the frequency nf0

60
Q

What is the equation for the fundamental frequency?

A

f = 1/2L * (T/μ)0.5

61
Q

What is Snell’s Law?

A

nisini = nrsinr

62
Q

What is the equation to find the fringe separation in a diffraction grating?

A

w = λD/s

  • D is distance between slit and screen and s is slit separation
  • D&raquo_space; s
63
Q

What is the equation to find the angle of diffraction of a beam?

A

dsinθ = n λ

64
Q

How do you find the split separation from lines per mm?

A

d = 1 / lines per metre || d = 1x10-3/ lines per mm

65
Q

What is the function of the core?

A
  • Propagate light by TIR
  • Have low absorption
  • Refractive index of core > cladding
66
Q

How is a stationary wave produced?

A
  • Waves travel to the boundaries and are reflected
  • Two waves travelling in opposite directions superpose/interfere
  • Fixed boundaries are nodes
  • In some positions the waves always interfere destructively causing nodes
  • In others they always interfere constructively causing antinodes
67
Q

What is the role of the outer sheath?

A

To prevent damage and crosstalk

Physics (5 decks)

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