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Physics⚡️ > Chapter 12 > Flashcards

Chapter 12 Flashcards

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1
Q

what are electromagnetic waves?

A

vibrations that don’t travel through a medium

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2
Q

what are mechanical waves?

A

vibrations that travel through a substance

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3
Q

examples of mechanical waves (2)

A

sound waves

seismic waves

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4
Q

examples of electromagnetic waves (2)

A

radio waves

light waves

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5
Q

what is the amplitude of a wave?

A

the distance from the distance line to the peak

the maximum displacement from its undisturbed position

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6
Q

what is the wavelength?

A

the distance between the same two point on two consecutive waves

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7
Q

what is frequency?

A

the number of waves passing through a certain point per second

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8
Q

what is frequency measured in?

A

Hertz (Hz)

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9
Q

what are the two types of waves?

A

longitudinal and transverse

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10
Q

equation for period of a wave

A

frequency

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11
Q

what is the period of a wave?

A

the time it takes to complete one full cycle of the wave

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12
Q

characteristics of transverse waves

A

oscillations are perpendicular to the direction of energy transfer
(they go up and down)

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13
Q

where do waves transfer energy?

A

in the direction they are travelling

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14
Q

characteristics of longitudinal waves

A

oscillations are parallel (along) the direction of travel

they go right and left

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15
Q

examples of transverse waves

A

electromagnetic waves

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16
Q

examples of longitudinal waves

A

sound waves

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17
Q

what does a large amplitude show?

A

the waves are carrying a lot of energy

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18
Q

what is the wave speed?

A

the distance travelled by a wave each second through a substance

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19
Q

how to calculate wave speed?

A

wave speed = frequency x wavelength

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20
Q

what is a rarefaction?

A

when the waves become more spread out

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21
Q

what is a compression?

A

when the waves get closer together

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22
Q

how to investigate reflection of waves?

A

use a ripple tank

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23
Q

what is refraction?

A

the change in direction of a wave when it crosses between medium

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24
Q

what is important to remember about the angle of incidence and reflection?

A

they are THE SAME

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25
Q

what are plane ?

A

they are straight

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26
Q

what is the angle of incidence?

A

the angle between the incoming wave and the normal

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27
Q

what is the angle of reflection?

A

the angle between the reflected wave and the normal

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28
Q

what is the normal?

A

an imaginary line that is perpendicular to the surface at the point of incidence

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29
Q

what does the amount by which a wave is refracted by depend on?

A

how much the wave speeds up or slows down

density of the two materials

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30
Q

what happens when a wave crosses a boundary and slows down?

A

it bends towards the normal

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31
Q

what happens when a wave crosses a boundary and speeds up?

A

it bends away from the normal

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32
Q

what happens to the frequency when a wave is refracted?

A

it stays the same

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33
Q

what is the optical density of a substance?

A

how well light can travel through it

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34
Q

what happens to the wavefronts in a denser material?

A

the waves slow down so they get closer together

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35
Q

what are the three things that can happen to a wave when it arrives at a boundary?

A

absorbed, transmitted, reflected

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36
Q

what are the two types of reflection

A

specular

diffuse

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37
Q

what is specular reflection?

A

when a wave is reflected in a single direction by a smooth substance

38
Q

what is diffuse reflection?

A

when light is reflected by a rough surface and the different rays are scattered in many different directions

39
Q

why does diffuse reflection occur?

A

the normal will be different for each ray because of the uneven surface
this means the angle of incidence and therefore reflection will be different for each ray

40
Q

what are sound waves caused by?

A

vibrations

41
Q

what are seismic waves?

A

the shock waves that are caused by an earthquake

42
Q

where are earthquakes generated?

A

in the earth’s crust

43
Q

what happens to waves when they arrive at a boundary? 5

A 
it can be completely reflected
partially reflected
refracted
absorbed
slow down
44
Q

what is the focus of an earthquake?

A

where it originates

45
Q

what is the epicentre of an earthquake?

A

the nearest point to the focus on the surface

46
Q

what are the 3 types of seismic waves?

A

Primary waves
Secondary waves
(Long waves)

47
Q

what do P waves do? 2

A

cause initial tremors lasting about a minute

push and pull on material as they move

48
Q

what do S waves do? 2

A

cause the aftershocks

move material side to side

49
Q

what do L waves do and where are they found?

A

earth’s crust

arrive last and shake material both up and down and side to side

50
Q

properties of P waves 3

A

longitudinal
travel very fast
travel through solids and liquids

51
Q

properties of S waves 3

A

transverse
slower than P waves
can’t travel through gases or liquids

52
Q

why do P and S waves bend as they travel through the mantel?

A

their speeds change with the increasing depth so their directions do too

53
Q

why do P waves refract at the boundary between the mantle and outer core?

A

the two have very different densities so the P waves’ speed changes abruptly and so does their direction

54
Q

why can’t S waves travel through the outer core?

A

they are transverse and can’t travel through liquid

55
Q

what is the shadow zone?

A

where no P or S waves are detected

56
Q

how was the boundary between the crust and mantle discovered?

A

when seismometers discovered that the speed of seismic waves changed at around 50 km below the surface

57
Q

how do we know that the inner core is solid?

A

weak P waves are detected in the shadow zone so we know that the core is solid and refracts P waves into this zone

58
Q

how does the existence of the shadow zone prove the existence of a liquid outer core? 2

A

S waves can’t travel through the outer core so aren’t detected
P waves are refracted at the boundary as they enter and leave the outer core. The second refraction is further around so they can’t reach the shadow zone

59
Q

what happens when seismic waves reach a boundary? 2

A

some will be absorbed and some will be refracted, so they change speed gradually

60
Q

what is the range of human hearing?

A

20 Hz - 20 KHz

61
Q

what are ultrasound waves?

A

waves above the highest frequency we can hear

62
Q

process of producing ultrasound

A

electrical devices produce electrical oscillations over a range of frequencies
these are converted into mechanical vibrations
this makes sound waves that are beyond our range of hearing

63
Q

what is partial reflection?

A

when a wave passes from one medium to another, so,e is reflected and some is transmitted or refracted

64
Q

how do ultrasounds measure internal boundaries?

A

when there is a boundary, some ultrasound is reflected back. The time taken is recorded and this is used to work out how far the boundary is

65
Q

how are ultrasound waves used for medical imaging?

A

wherever there is a boundary, some of the wave is reflected back and detected
the timing and distribution of these echoes are recorded and turned into an image

66
Q

how are ultrasound waves used in industrial imaging?

A

ultrasound waves will normally be reflected by the far side of the material
if there is a crack/flaw, they will be reflected sooner

67
Q

what is echo sounding and how does it work?

A

it uses high frequency sound waves to measure the depth of water under a vessel or to locate an object

68
Q

2 advantages of ultrasound used for medical scanning

A

reflected at boundaries (can scan soft tissues)

non ionising - not harmful

69
Q

what is non ionising radiation?

A

radiation that doesn’t have the energy to ionise an atom (remove an electron)

70
Q

how to calculate distance travelled by a wave (m)?

A

speed of ultrasound waves x time taken

71
Q

how to calculate the depth of a boundary below a surface? (m)

A

0.5 x speed of wave x time taken

72
Q

why are musical notes easy to listen to?

A

they are rhythmic with a regular wave pattern

73
Q

what is general noise made of?

A

sound waves that randomly vary in frequency

74
Q

what are sound waves caused by?

A

vibrating objects

75
Q

what type of wave is sound?

A

longitudinal

76
Q

how are vibrations passed through a medium?

A

through a series of rarefactions and compressions

77
Q

why do sound waves refract when they enter different media?

A

they speed up

their wavelength changes but frequency remains the same so speed must also change

78
Q

how do we hear?

A

sound waves reach ear drum
vibrations passed through ear drum into cochlea
cochlea turns these vibrations into electrical signals to brain

79
Q

why is the frequency of human hearing limited?

A

the conversions of sound waves to vibrations only works over a limited range

80
Q

how does echo sounding work?

A

high frequency sound waves are transmitted
they reflect from the hard, flat surface
these echoes are detected by a receiver

81
Q

why do sounds move slower in gases (and don’t travel in a vacuum)?

A

there are no/few particles to vibrate

82
Q

how does a vibration work?

A

the compressions and rarefactions make the particles vibrate and move
these vibrations make others move and so the sound travels

83
Q

what to use to investigate water waves?

A

a ripple tank

84
Q

what to use to investigate sound waves?

A

a loudspeaker and signal generator

85
Q

what to use to investigate waves in a solid?

A

a stretched spring

86
Q

how to explain rarefaction?

A

the wavefronts move slower in a denser medium (or vice versa)
so they are closer together and are at a smaller angle to the boundary than the angle of incidence
they have the same frequency but different speeds, so have different wavelengths

87
Q

what happens to a substance when it absorbs waves and why?

A

it heats up because it takes the energy from the waves

88
Q

what happens to waves travelling through a solid and why?

A

their amplitude decreases - the solid absorbs the energy

89
Q

what happens when waves cross a boundary perpendicularly?

A

they don’t change direction but their speed changes

90
Q

What happens when a material absorbs radio waves?

A

Creates an alternating current with the same frequency as the radio wave

Physics⚡️ (16 decks)

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