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Physics > Waves and Optics > Flashcards

Waves and Optics Flashcards

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1
Q

What is a longitudinal wave?

A

The vibrations or displacement are parallel to the direction of energy transfer.

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2
Q

What is a transverse wave?

A

A wave where the displacement or vibrations to the direction of energy transfer.

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3
Q

What is a progressive wave?

A

A progressive wave transfers energy without the permanent displacement of matter and is made up of particles oscillating.

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4
Q

What is the amplitude of the wave?

A

A wave’s maximum displacement from the equilibrium position (m)

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5
Q

What is frequency?

A

The number of complete oscillations passing through a point per second. (Hz)

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6
Q

What is the wavelength of a wave?

A

The length of one whole oscillation (m)

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7
Q

What is wave speed and how is it calculated?

A

v = fλ

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8
Q

What is a transverse wave?

A

A type of wave where energy moves perpendicular to the oscillations

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9
Q

What is the time period?

A

The time taken for one whole oscillation

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10
Q

What is constructive interference?

A

When 2 or more waves have displacement in the same direction

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11
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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12
Q

What is a node (waves)?

A

Region of no displacement

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13
Q

What is an antinode?

A

Region of maximum displacement

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14
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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15
Q

How do you determine the resultant displacement after interference?

A

The vector sum of displacements?

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16
Q

What is a stationary wave?

A

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

17
Q

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

A

An integer number of half wave lengths

18
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.
19
Q

What are coherent waves?

A

Waves of a fixed phase relationship and same frequency.

20
Q

What is refraction?

A

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

21
Q

What is the refractive index of air?

A

1

22
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)

23
Q

Why does a perpendicular ray not refract?

A

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

24
Q

What is the relationship between frequency and refraction?

A

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

25
Q

What is the critical angle of incidence?

A

One where the angle of refraction is 90 degrees

26
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
27
Q

What happens if we exceed the critical angle?

A

Total internal reflection

28
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
29
Q

How can we deal with pulse absorption?

A
  • Use repeaters
  • Increase the intensity of the pulse
  • Use a beam that diffracts less
30
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
  • Violet has the greatest change in speed and red the least
  • Violet travels slower than red
  • A broadened signal is received by the sensor
31
Q

Describe Pulse Broadening.

A
  • Pulse is wider as the pulse arrives at different times
  • Pulse is shorter as there is a lower intensity as less energy is arriving per second
32
Q

What is the solution to spectral/material dispersion?

A

Use a monochromatic source of light

33
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
34
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
35
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
36
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
37
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
38
Q

What are some of the required properties of the cladding?

A
  • Lower refractive index than the core
  • High enough refractive index so the high incidence rays are not totally internally reflected and are lost in the cladding
39
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

Physics (5 decks)

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