Waves Flashcards

1
Q

what is amplitude?

A

the greatest displacement of a wave, measured from the midpoint

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2
Q

what is the wavelength?

A

the length of one oscillation (cycle) of a wave - the distance from a point on one qave to the equivalent point on the adjacent wave

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3
Q

what is frequency?

A

the number of oscillations (cycles) of a wave per second, measured in Hertz (1 Hz is one oscillation per second)

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4
Q

what is the time period?

A

time for one oscillation (cycle) of a wave

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5
Q

how do you calculate period?

A

1 / frequency

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6
Q

how do you calculate wave speed?

A

frequency x wavelength

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7
Q

what is the rest position?

A

the undisturbed position of particles or fields when they are not vibrating

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8
Q

what is displacement?

A

the distance that a certain point in the medium has moved from its rest position

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9
Q

what is a peak?

A

the highest point above the rest position

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10
Q

what is a trough?

A

the lowest point below the rest position

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11
Q

do electromagnetic waves need a medium to travel through?

A

no

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12
Q

do mechanical waves need a medium to travel through ?

A

yes

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13
Q

are frequency and wavelength directly or inversely proportional ?

A

inversely

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14
Q

do transverse waves oscillate perpendicular or parallel to the direction of energy transfer?

A

perpendicular

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15
Q

longitudinal waves oscillate perpendicular or parallel to the direction of energy transfer?

A

parallel

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16
Q

what are some examples of transverse waves?

A
  • light
  • all EM waves
  • ripples on water
  • S waves (seismic)
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17
Q

what are some examples of longitudinal waves?

A
  • sound
  • ultrasound
  • pressure waves
  • P waves (seismic)
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18
Q

what is a compression?

A

Region in a longitudinal wave where the particles are closest together.

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19
Q

what is a rarefaction?

A

regions in a longitudinal wave of low pressure due to particles being spread further apart

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20
Q

angle of incidence = ?

A

angle of reflection

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21
Q

what happens when light passes through an object?

A

some of the light is reflected, some of the light is transmitted, and a small amount may be absorbed

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22
Q

what is specular reflection?

A

reflection from a smooth surface which gives a sharp image

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23
Q

what is diffuse reflection?

A

reflection from a rough surface - light is scattered in lots of different directions

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24
Q

what happens as light passes from air into glass?

A

it moves towards the normal (AOI is greater than AOR)

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25
Q

what happens as as light passes from glass into air?

A

it moves away from the normal (AOI is less than AOR)

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26
Q

why does light refract?

A

due to a change in speed when it enters an optically denser material

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27
Q

what is the speed of sound in air?

A

330 m/s

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28
Q

why does sound travel faster in solids and liquids?

A

because it will be transmitted through the material faster as the particles are much closer together

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29
Q

how do ears detect sound?

A
  • Sound waves enter the ear canal and cause the eardrum to vibrate.
  • Three small bones transmit these vibrations to the cochlea.
  • This produces electrical signals which pass through the auditory nerve to the brain, where they are interpreted as sound.
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30
Q

what is the human hearing range?

A

20Hz to 20000 Hz

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31
Q

what is ultrasound?

A

sound waves with a frequency over 20kHz or 20,000 Hz

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32
Q

why is ultrasound useful?

A

it is not ionising or heating

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33
Q

what is ultrasound used for?

A
  • medical scans
  • cleaning medical equipment and jewellery
  • finding flaws in metal
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34
Q

how can ultrasound be used to detect flaws?

A
  • when ultrasound reaches a boundary between two substances with different densities, they are partly reflected back and the remainder of the waves pass through
  • detector placed near source of waves detects the reflected waves
  • detector measures the time between a wave leaving the source and reaching the detector - the further the boundary, the longer the time between leaving the source and reaching the detector
  • if wave takes less time than usual to reflect back, something must have been in the way to reflect this wave - therefore there is a flaw there
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35
Q

describe the structure of the earth

A
  • solid inner core
  • liquid outer core
  • solid mantle
  • solid crust
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36
Q

what are the 2 types of seismic waves?

A
  • primary waves (P waves)
  • transverse waves (S waves)
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37
Q

what are primary waves?

A
  • travel faster
  • are detected first
  • longitudinal waves
  • travel through outer liquid core as can pass through both solids and liquids
38
Q

what are transverse waves?

A
  • travel more slowly
  • are detected later
  • don’t travel through outer liquid core as can only pass through solids
39
Q

how do seismic waves help scientists understand the structure of the earth?

A

P waves refract at the core and S waves can’t be detected on the opposite side of the earth

40
Q

what is the electromagnetic spectrum?

A

a range of frequencies of electromagnetic waves, ranging in wavelength from 1x10^-4m to 1x10^-15m

41
Q

what types of waves are electromagnetic waves?

A

transverse (that transfer energy from the source of the waves to an absorber)

42
Q

can EM waves travel through vacuums?

A

yes

43
Q

do EM waves travel in different speeds through a vacuum or air?

A

no, they travel at the same speed through a vacuum or the air

44
Q

do all types of electromagnetic waves travel at the same or different velocities through a vacuum?

A

same - speed of light

45
Q

list the electromagnetic spectrum from long wavelength and low frequency to short wavelength and high frequency

A
  • radio waves
  • microwaves
  • infrared radiation
  • visible light
  • ultraviolet light
  • x rays
  • gamma rays
46
Q

what are the uses and dangers of radio waves?

A
  • communication systems in radio and television
  • heating (minimal)
47
Q

what are the uses and dangers of microwaves?

A
  • heating food, satellite communications
  • heating
48
Q

what are the uses and dangers of infrared radiation?

A
  • electrical heaters, remote controls, cooking food, infrared cameras
  • heating
49
Q

what are the uses and dangers of of visible light?

A
  • seeing
  • blinding
50
Q

what are the uses and dangers of ultraviolet light?

A
  • sterilisation, sun tanning, energy efficient lamps
  • ionisation
51
Q

what are the uses and dangers of x-rays?

A
  • seeing bones and other medical scans, luggage scans for bombs
  • ionisation
52
Q

what are the uses and dangers of gamma rays?

A
  • cancer treatment
  • ionisation
53
Q

what properties make radio waves useful for use in radios?

A
  • transmitted easily through air.
  • do not cause damage if absorbed by the human body
  • can be reflected to change their direction.
54
Q

how are radio waves produced and used?

A
  • by oscillations in electrical circuits.
  • When radio waves are absorbed by a conductor, they create an alternating current.
  • This electrical current has the same frequency as the radio waves.
  • Information is coded into the wave before transmission, which can then be decoded when the wave is received.
55
Q

how do microwaves work?

A
  • High frequency microwaves have frequencies which are easily absorbed by molecules in food.
  • The internal energy of the molecules increases when they absorb microwaves, which causes heating.
56
Q

how does infrared radiation cause heating?

A
  • it has frequencies which are absorbed by some chemical bonds
  • the internal energy of the bonds increases when they absorb infrared light, which causes heating.
57
Q

how do fibre optic communications work?

A

coded pulses of light travel through glass fibres from a source to a receiver.

58
Q

how is ultraviolet light used to create energy efficient lamps?

A

Fluorescent substances absorb ultraviolet light produced inside the lamp, and re-emit the energy as visible light.

59
Q

what properties of x rays make them useful for internal imaging?

A

they are transmitted through body tissues with very little absorption but are absorbed by dense structures like bones

60
Q

what is the wavelength of visible light?

A

400nm (violet) to 700nm (red)

61
Q

what are primary light colours?

A

red, green and blue

62
Q

what are the secondary light colours?

A

cyan, magenta and yellow

63
Q

how do TV screens produce colour?

A

consist of tiny RGB pixels and varying the brightness of each produces every what we see as every other colour of light

64
Q

how do we observe the colour of an object?

A

due to the wavelengths of light that it reflects.

65
Q

what primary colours will be reflected and absorbed from a red object?

A

reflects: red - absorbs: green, blue

66
Q

what primary colours will be reflected and absorbed from a green object?

A

reflects: green - absorbs: red, blue

67
Q

what primary colours will be reflected and absorbed from a blue object?

A

reflects: blue - absorbs: red, green

68
Q

what primary colours will be reflected and absorbed from a cyan object?

A

reflects: green and blue - absorbs: red

69
Q

what primary colours will be reflected and absorbed from a magenta object?

A

reflects: red and blue - absorbs: green

70
Q

what primary colours will be reflected and absorbed from a yellow object?

A

reflects: red and green - absorbs: blue

71
Q

what primary colours will be reflected and absorbed from a white object?

A

reflects: red, blue, green - absorbs: none

72
Q

what primary colours will be reflected and absorbed from a black object?

A

reflects: none - absorbs: green, red, blue

73
Q

if a red light shines on a red object, what colour will the object appear?

A

red

74
Q

if a red light shines on a white object, what colour will the object appear?

A

red

75
Q

if a blue light shines on a red object, what colour will the object appear?

A

black

76
Q

if a blue light shines on a cyan object, what colour will the object appear?

A

blue

77
Q

if a green light shines on a magenta object, what colour will the object appear?

A

black

78
Q

if a yellow light shines on a green object, what colour will the object appear?

A

green

79
Q

how do filters work?

A

Filters selectively allow transmission of certain frequencies of while absorbing others.

80
Q

what is a convex lens?

A

is fatter at the middle and converges light

81
Q

what is a concave lens?

A

is fatter at the edges and diverges light

82
Q

where are the principle focusses?

A

on each side of a lens

83
Q

in light ray diagrams, if the image is formed where 2 rays of light meet what kind of image is it?

A

real

84
Q

in light ray diagrams, if the image is formed from a dashed line because the 2 rays diverge, what kind of image is it?

A

virtual

85
Q

what are the words used to label images in light ray diagrams?

A

real or virtual, magnified or diminished, upright or inverted

86
Q

what is the principal focus?

A

the focal point: where light rays diverge from or converge towards

87
Q

what is a real image?

A

An image formed when light rays actually meet at a point - can be projected on a screen

88
Q

what is the focal length?

A

Distance between a focal point and the centre of a lens or mirror.

89
Q

what is a virtual image?

A

An image formed by the apparent intersection of light rays - cannot be projected on a screen.

90
Q

what is the magnification equation?

A

Magnification = image size / object size

91
Q
A