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Waves And Optics Flashcards

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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
What is the role of the cladding in a fibre optic cable?
- 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
26
How can we deal with pulse absorption?
- Use repeaters - Increase the intensity of the pulse - Use a beam that diffracts less
27
Describe Spectral/Material Dispersion in reference to fibre optics.
- 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
28
Describe the results of Pulse Broadening.
- Pulse is wider as the pulse arrives at different times - Pulse is a lower intensity as less energy is arriving per second
29
What is the solution to spectral/material dispersion?
Use a monochromatic source of light
30
Describe Modal Dispersion
- 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
How is Modal Dispersion reduced?
- 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
Why do diamonds sparkle?
- 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
What are some of the required properties of the core?
- Material should have a low absorption - Refractive index should not vary much across the wavelengths of light that are to be used
34
What are some of the properties of the cladding?
- 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
Why do we want to reduce pulse broadening?
Prevent individual pulses in a series from overlapping so that we get a clearer signal
36
What is diffraction?
The change in direction of waves when they encounter an obstacle or pass through an aperture
37
What is a diffraction grating?
Specially constructed pieces of glass which have many tiny apertures. Grating spacing given in lines per mm.
38
When is the effect or diffraction greatest?
When the aperture size is equal to the wavelength
39
When do we get an interference pattern?
If two coherent light-waves diffract through two apertures.
40
When asked to describe Young’s slits or a diffraction grating what kind of terms should you use?
- coherent - monochromatic - wavelength - path difference - interference
41
How do you describe white light that is shone through a slit?
- Central maximum is white - Next fringe is a gradient, from blue to red, inside out
42
What is spectrometry?
Light emitted, reflected, or absorbed by a material can give useful information about its structure or composing elements.
43
What is Huygen’s Principle?
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
What are the differences between single slit interference and Young’s slits?
- 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
What is incident light?
Light that approaches an inter-medium boundary
46
What is light?
An electromagnetic wave
47
What is absorption of light?
Energy transferred into a store, usually thermal/kinetic energy
48
What are electromagnetic waves composed of?
Oscillating electric and magnetic fields. Their oscillations are perpendicular to each other and the direction of travel.
49
What determines the plane of polarisation?
The electric field’s plane of oscillation
50
What is a polarising filter?
A filter that only transmits one polarisation of light
51
How can we calculate the amplitude of a wave after it has passed through a polarised filter?
Find the component of the light wave that is parallel to the direction of polarisation
52
What are the key points to mention when asked a polarisation question?
- 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
How can we determine where interference will occur in Young’s slits?
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
What can we talk about when considering two points on a stationary wave?
- Fixed phase relationships (mention if it is in phase or not) - Amplitudes - Frequencies - Oscillation speeds
55
What are the requirements for a stationary wave?
- Same wave speed - Moving in opposite directions - Same wavelength/frequency
56
What equation links period and frequency?
p = 1/f
57
What equations links wave speed, frequency and wavelength?
c = λf
58
What is the distance between adjacent nodes in a stationary wave?
λ/2
59
How does frequency change as the harmonic increases?
The nth harmonic has the frequency nf0
60
What is the equation for the fundamental frequency?
f = 1/2L * (T/μ)0.5
61
What is Snell’s Law?
nisini = nrsinr
62
What is the equation to find the fringe separation in a diffraction grating?
w = λD/s - D is distance between slit and screen and s is slit separation - D >> s
63
What is the equation to find the angle of diffraction of a beam?
dsinθ = n λ
64
How do you find the split separation from lines per mm?
d = 1 / lines per metre || d = 1x10-3/ lines per mm
65
What is the function of the core?
- Propagate light by TIR - Have low absorption - Refractive index of core > cladding
66
How is a stationary wave produced?
- 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
What is the role of the outer sheath?
To prevent damage and crosstalk
68

Physics (6 decks)

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