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waves Flashcards

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1
Q

what is a progressive wave

A
  • transfers energy without transferring material
  • made up of particles oscillating
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2
Q

properties of waves in phase

A
  • same displacement and velocity
  • same frequency and wavelength
  • phase difference will be multiple of 360 degrees, 2pi radians, or 1 wavelength
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3
Q

properties of waves out of phase

A
  • odd integer of half cycles apart
  • phase difference is multiples of 180 degrees, 1pi radians (odd), half a wavelength
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4
Q

properties of a transverse wave

A
  • oscillates at right angle to direction of energy propagation
  • travel in vacuum
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5
Q

examples of transverse wave

A
  • EM waves
  • s waves
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6
Q

properties of a longitudinal wave

A
  • oscillates parallel to the direction of energy propagation
  • compressions and rarefactions
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7
Q

examples of longitudinal waves

A
  • sound waves
  • p waves
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8
Q

polarised wave

A
  • only travels in one plane (vertical/horizontal)
  • transverse
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9
Q

application of polarised waves

A
  • polaroid sunglasses
  • tv and radio signals
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10
Q

what is superposition

A

displacement of 2 waves are combined as they pass

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11
Q

what is the resultant displacement of a superposed wave

A

vector sum of each wave’s displacement

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12
Q

what is constructive interference

A

2 waves have displacement in the same direction

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13
Q

what is destructive interference

A

when 2 waves have opposite displacements

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14
Q

how is a stationary wave formed

A
  • superposition of 2 progressive waves
  • opposite directions
  • same frequency, wavelength and amplitude
  • no energy transfer
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15
Q

properties waves in phase

A
  • constructive interference
  • antinodes are formed
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16
Q

properties of waves out of phase

A
  • destructive interference
  • nodes are formed
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17
Q

what is the first harmonic

A

the lowest frequency at which a stationery wave is formed

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18
Q

examples of stationary waves

A
  • stationary microwaves
  • stationary sound waves
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19
Q

what is path difference

A

difference in distance travelled by two waves

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20
Q

what is a coherent light source

A
  • same frequency and wavelength
  • fixed phase difference
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21
Q

give an example of a coherent light source

A

laser

22
Q

what is diffraction

A

the spreading of waves around a boundary

23
Q

how does wavelength affect diffraction

A
  • gap size < wavelength (reflected waves)
  • gap size = wave length (strong diffraction)
  • gap size > wavelength (very weak diffraction)
24
Q

what does the pattern look like when a monochromatic light is diffracted

A
  • central bright fringe (double size as others)
  • alternating bright and dark fringes on either side
25
Q

what do bright and dark fringes show

A

bright - constructive interference + waves in phase
dark - destructive interference + waves completely out of phase

26
Q

what diffraction pattern occurs from white light?

A
  • spectrum of colour
  • central white maximum
  • alternating bright fringes (spectra)
  • violet is closest to center + red furthest away
27
Q

how can you vary the width of the central maximum?

A
  • increase slit width to decrease diffraction (narrower centre + more intensity)
  • increase wavelength to increase diffraction (wider centre + less intensity)
28
Q

what is a diffraction grating?

A

a slide containing many equally spaced slits very close together

29
Q

what happens when monochromatic light is shone through a diffraction grating

A

the interference pattern is much sharper and brighter because of more rays of light reinforcing the pattern

30
Q

what is the ray of light passing through the centre of the diffraction grating called

A

zero order line

31
Q

applications of diffraction gratings

A
  • split up light from stars to get line absorption spectra + shows elements present in the star
  • x-ray crystallography
32
Q

what is a refractive index

A
  • measures how much a material slows down light passing through it
  • speed of light in vacuum / speed of light in medium
  • n = c/cs
33
Q

a material with a higher refractive index is ____ dense

A

more

34
Q

what is the refractive index of air

A

approx. 1

35
Q

what is refraction

A

the bending of light as it enters a new medium (change of direction)

36
Q

what is snell’s law

A

n1sinθ1 = n2sinθ2

37
Q

how does light bend when entering a more dense material?

A

bends towards the normal

38
Q

how does light bend when entering a less dense material?

A

bends away from the normal

39
Q

what happens when the angle of refraction is exactly 90°?

A
  • light is refracted along the boundary
  • incident angle is critical
40
Q

when does total internal reflection occur?

A
  • angle of incidence is greater than critical angle
  • incident refractive index > refractive index of material at boundary
41
Q

application of total internal reflection

A

optical fibres

42
Q

features of optical fibres

A
  • optically dense core with lower dense cladding
  • cladding protects the core from damage
  • cladding prevents signal degradation through light escaping from the core
43
Q

what can signal degradation be caused by?

A
  • absorption
  • dispersion
44
Q

types of dispersion

A
  • modal
  • material
45
Q

what is absorption?

A
  • part of the signal’s energy is absorbed by the fibre
  • reducing the amplitude
  • information is lost
46
Q

what is dispersion?

A
  • causes pulse broadening (signal is received broader than original signal)
  • can overlap causing information loss
47
Q

what is modal dispersion?

A
  • light rays enter fibre at different angles (take different paths)
  • rays take a different amount of time to travel, causing pulse broadening
48
Q

how can modal dispersion be reduced?

A
  • make the core really narrow
  • makes the possible difference in path lengths smaller
49
Q

what is material dispersion?

A
  • caused by using light of different wavelengths
  • light rays travel at different speeds, causing pulse broadening
50
Q

how can material dispersion be reduced?

A

using monochromatic light

51
Q

how can absorption and dispersion be reduced?

A
  • using an optical fibre repeater
  • regenerates signal during its travel to its destination

physics (9 decks)

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