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Physics > Waves > Flashcards

Waves Flashcards

1
Q

what do all waves do

A

transfer energy from one place to another

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2
Q

what is a transverse wave

A

a wave where oscillations are perpendicular to the direction of energy transfer

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3
Q

what is a longitudinal wave

A

a wave where oscillations are parallel to the direction of energy transfer

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4
Q

what do all longitudinal waves need

A

a medium to travel in

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5
Q

example of transverse wave

A

light, electromagnetic wave

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6
Q

example of longitudinal waves

A

sound waves

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7
Q

features of transverse waves

A

have peaks and troughs

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8
Q

features of longitudinal waves

A

have compressions and rarefactions

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9
Q

what is important to know about the movement of waves

A

the wave moves and not whatever it passes through

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10
Q

what is amplitude

A

maximum displacement of a point on a wave away from its undisturbed position

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11
Q

what is wavelength

A

the distance from a point on one wave to the equivalent point on the adjacent wave

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12
Q

what is frequency

A

the number of waves passing a point each second

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13
Q

what is the unit of waves

A

Hz

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14
Q

what is period

A

the time for one wave to pass a point

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15
Q

wave speed equation

A

wave speed = frequency x wavelength

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16
Q

period equation

A

period = 1/ velocity

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17
Q

what is wave speed

A

the speed at which the wave moves through the medium

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18
Q

method to measure speed of sound waves in air

A
  1. one person stands 100m from a large flat wall
  2. the person claps and another person measures the time taken to hear the echo
  3. calculate speed using distance x time
  4. distance is double because the wave has travelled to the wall and back
  5. repeat to reduce human error
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19
Q

what determines how quickly sound waves travel

A

the density of the medium

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20
Q

where do sound waves travel fastest

A

a solid as spaces between particles is smaller so vibrations and energy can be passed on more quickly

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21
Q

what is the speed of sound in air

A

330m/s

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22
Q

Ripple tank practical method

A
  1. Fill the ripple tank of water to 5mm and place it on top of a piece of white paper
  2. place a vibrating bar on the surface of the water and attach it to a power pack
  3. place a lamp above the ripple tank
  4. turn on the power so the bar vibrates creating waves across the water surface
  5. to measure wavelength place a metre ruler on paper and use a stroboscope to freeze the wave patterns - measure as many wavefronts as possible and divide by the number of waves
  6. to measure frequency, place a timer next to the paper and count the number of waves passing a point in 10 seconds
  7. to calculate wave speed multiply the wavelength by the frequency
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23
Q

Waves in a solid practical method

A
  1. attach a string at one end to a vibration generator, other end to a hanging mass to keep string taut
  2. attach vibration generator to a signal generator
  3. produce a standing wave on vibrating string by adjusting the frequency
  4. to measure wavelength use a metre ruler to measure across multiple standing waves and divide by number of total waves
  5. to measure frequency use a stopwatch to time wave oscillations over 10 cycles and divide value by 10 to find the time period and put into frequency equation
  6. to calculate wave speed multiply wavelength by frequency
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24
Q

safety precautions of wave practicals

A

take care working with water and electricity - mop up spillages
don’t stand beneath masses in case weights fall off
wear safety goggles when using oscillating string as it may snap at high frequency

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25
Q

what changes in sound waves when they move from one medium to another

A

wave speed
frequency
wavelength

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26
Q

where do sound waves travel slowest

A

gasrd

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27
Q

how do sound waves transfer energy

A

by the molecules vibrating and knocking into neighbouring particles

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28
Q

how is the relationship between wave speed , wavelength and frequency determined

A

using wave speed = frequency x wavelength

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29
Q

what can the change in velocity of a sound wave result in

A

a change of direction of the sound wave (refraction)

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30
Q

what happens when sound moves from a denser medium to a less dense medium

A

the wavelength of the sound wave decreases
the frequency of the sound wave stays the same
the velocity of the sound wave decreases

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31
Q

what happens when sound waves move from a less dense medium to a denser medium

A

the wavelength of the sound wave increases
the frequency of the sound wave stays the same
the velocity of the sound wave also increases

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32
Q

what is the speed of sound in air affected by

A

temperature

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33
Q

what happens to the speed of sound on warm days

A

air molecules move faster so they carry sound waves faster increasing speed of sound

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34
Q

what happens to the speed of sound on cold days

A

air molecules move at a slower pace so they carry sound waves at a slower pace decreasing the speed of sound

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35
Q

what happens as frequency of a wave increases

A

velocity increases

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36
Q

what happens as wavelength increases

A

velocity increases

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37
Q

what is period inversely proportional to

A

frequency

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38
Q

what does a smaller wave period mean

A

higher frequency, greater velocity

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39
Q

what can happen to waves at the boundary between two materials

A

reflected
absorbed
transmitted

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40
Q

features of reflection of waves

A

-waves will reflect off a flat surface
-the smoother the surface, the stronger the reflected wave is
-rough surfaces scatter the light in all directions so they appear matt and not reflective
-the angle of incidence = angle of reflection
-light will reflect if the object is opaque and is not absorbed by the material as the electrons will absorb the light energy and remit it as a reflected wave

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41
Q

features of transmission of waves

A
  • waves will pass through a transparent material
    -the more transparent the more light will pass through the material
    -it can still refract but the process of passing through the material and still emerging is transmission
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42
Q

features of absorption of waves

A

-if the frequency of light matches the energy levels of the electrons
the light will be absorbed by the electrons and not re-emitted
they will be absorbed and then re-emitted over time as heat
so that particular frequency has been absorbed
if a material appears green, only green light has been reflected ad the rest of the frequencies in visible light have been absorbed

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43
Q

what happens when sound waves travel through solids

A

they cause vibrations in the solid

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44
Q

how does the body collect sound

A

the outer ear collects the sound and channels it down the ear canal

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45
Q

what kind of wave is a sound wave as it travels down the ear canal

A

it is still a pressure air wave

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46
Q

what happens when the sound waves hit the eardrum

A

tightly stretched membrane vibrate as the incoming pressure waves reach it making
compression forces the eardrum inward
rarefaction forces the eardrum outward due to pressure
so the eardrum vibrates at the same frequency as the sound wave
the small bones connected to this also vibrate at the same time (stirrup bone)

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47
Q

where is the vibrations in the bones from a sound wave transmitted to

A

the fluid in the inner ear

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48
Q

where are compression waves transferred to in the ear

A

the fluid in the cochlea

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49
Q

what happens as the fluid moves in the ear

A

the small bones act as an amplifier of the sound waves
as the fluid moves due to the compression waves, the small hairs that line the cochlea move too
each hair from nerve cells is sensitive to different sound frequencies so some move more than others for certain frequencies
when a certain frequency is received the hair attuned to that frequency moves a lot releasing an electrical impulse to the brain which is interpreted as a sound

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50
Q

what is human hearing range

A

20Hz to 20kHz

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51
Q

what can happen in the ear that affects human hearing

A

in the cochlea the hairs attuned to higher frequencies die or get damaged

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52
Q

what are causes of hairs attuned to higher frequencies dying or becoming damaged

A

constant loud noise damaging the hairs over the years
changes in the inner ear as growing older
smoking, chemotherapy, diabetes

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53
Q

why have humans evolved to hear this range of frequencies

A

it gives the greatest survival advantage

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54
Q

why can humans not hear ultrasound

A

we do not use sonar to hunt , we have accurate vision instead of

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55
Q

what happens when ultrasound reaches a boundary between two media

A

they are partially reflected back

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56
Q

what happens to the remainder of the waves that are not reflected back in ultrasound

A

they continue and pass through so a receiver next to the emitter can record the reflected waves

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57
Q

how does the receiver show the distance from the source the waves are

A

the speed of the waves are constant so measuring the time between emission and detection can show distance

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58
Q

how can ultrasound be used for imaging under surfaces

A

a crack in a metal block will cause some waves to reflect earlier than the rest so will show up

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59
Q

what is infrasound/ seismic waves

A

a sound wave with a frequency lower than 20Hz

60
Q

what are the two seismic waves

A

P and S waves

61
Q

features of P waves

A

longitudinal and can pass through solids and liquids

62
Q

features of S waves

A

transverse and only pass through solids , slower than P waves, bent by changing density of a rock

63
Q

features of an L wave

A

arrive last and cause vigorous movement on the surface
travel more slowly than P waves and S waves

64
Q

why do p and s wave bend towards the surface of the earth as they travel through the earth

A

their speed and direction changes at different densities (refraction)

65
Q

why do seismic waves prove the structure of the earths core

A

there is a liquid core under the mantle because S waves do not travel through the outer core as they cannot travel through liquid

66
Q

what is echo sounding

A

using high frequency sound waves

67
Q

what is echo sounding used for

A

detecting objects in deep water such as shoal of fish
or detecting how far the seabed is below the ship

68
Q

how does echo sounding work

A

pule of ultrasound is sent below a ship and the time taken for it to reflect and reach the ship is used to calculate the depth

69
Q

what are electromagnetic waves

A

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

70
Q

what do electromagnetic waves form

A

a continuous spectrum

71
Q

features of electromagnetic waves

A

do not need particles to move
in space they all have the same velocity (speed of light)
can transfer energy from a source to an absorber
transverse waves

72
Q

examples of electromagnetic waves transferring energy from a source to an absorber

A

microwave source to food
sun emits energy to earth

73
Q

how are the waves grouped in the electromagnetic spectrum

A

long to short wavelength
low to high frequency

74
Q

electromagnetic spectrum order

A

radio waves
microwaves
infrared
visible light
ultraviolet
x rays
gamma rays

75
Q

why do our eyes only detect a limited range of electromagnetic waves

A

they can only detect visible light

76
Q

what does speed being constant for all EM waves result in

A

as wavelength decreases, frequency must increase
as frequency increases , energy of the wave increases

77
Q

what happens to refraction entering a denser material

A

it bends towards the normal

78
Q

what happens to refraction if entering a less dense material

A

it bends away from the normal

79
Q

what will substances do with EM waves depending on wavelength

A

absorb
transmit
refract
reflect

80
Q

glass reacting to em waves

A

transmit/ refract visible light
absorb uv radiation
reflect ir radiation

81
Q

why do material interact differently for different parts of the EM spectrum

A

the wavelengths and frequencies are different

82
Q

what are some effects on objects from the EM spectrum due to

A

differences in velocity

83
Q

why are some effects due to differences in velocity

A

when light enters a denser medium it slows down
shorter wavelengths slow down more than longer wavelengths

84
Q

why does dispersion occur of white light into a prism

A

the different wavelengths refract to a different amount therefore spread put creating a rainbow effect

85
Q

what happens when refracting

A

the speed decreases and wavelength decreases too in denser materials

86
Q

how are radio waves produced

A

oscillations in electrical circuits

87
Q

what happens when radio waves are absorbed

A

they create an alternating current at the same frequency as the radio waves

88
Q

what happens when electrons move to a higher orbit (further from nucleus)

A

the atom has absorbed em radiation

89
Q

what happens when electrons fall to a lower orbit (closer tot he nucleus

A

the atom has emitted em radiation

90
Q

what happens if an electron gains enough energy

A

it can leave the atom to form an ion

91
Q

what do gamma rays originate from

A

changes in the nucleus of an atom

92
Q

which em waves can have hazardous effects on human body tissue

A

uv light
x rays
gamma

93
Q

what does the effect of harmful em waves on the body depend on

A

the type of radiation and the size of the dose

94
Q

what does radiation dose mean

A

the risk of harm resulting from an exposure of the body to radiation

95
Q

how does uv radiation harm humans

A

skin ages prematurely increasing risk of skin cancer

96
Q

how is damage from uv radiation prevented

A

suncream prevents overexposure

97
Q

how does x ray and gamma ray harm humans

A

ionising radiation so can cause mutation of genes which causes cancer

98
Q

how is harm from x rays and gamma rays prevented

A

minimal exposure should be ensured

99
Q

what are radio waves used for

A

TV and radio

100
Q

why are radio waves used for TV and radio

A

long wavelength, can travel far without losing quality

101
Q

what are microwaves used for

A

satellite communication
cooking food

102
Q

why are microwaves used for satellite communication and cooking food

A

can penetrate the atmosphere to reach satellites

103
Q

what ir IR radiation used for

A

cooking food
infrared cameras

104
Q

why is ir radiation used to cook food and for ir cameras

A

transfers thermal energy

105
Q

what is visible light used for

A

fibre optics

106
Q

why is visible light used for fibre optics

A

best reflection/ scattering in glass (others have too short/long wavelengths)

107
Q

what is uv light used for

A

sun tanning
energy efficient lamps

108
Q

why is uv used for sun tanning and energy efficienct lamps

A

radiates the least heat but more energy

109
Q

what is x ray and gamma ray used for

A

medical imaging and treatment

110
Q

why is x ray and gamma ray used for medical imaging and treatment

A

very high in energy and can penetrate material easily

111
Q

what happens if light passes through the centre of a lens

A

it does not change direction

112
Q

what are focal points

A

points either side of the lens which light can converge at

113
Q

what can convex lenses have

A

virtual or real images

114
Q

what images to concave lenses have

A

virtual images

115
Q

features of a concave lens

A

caves inward
thinner at the centre than edges
spreads light outwards
light appears to have come from the focal point of

116
Q

what do concave lenses do

A

spread out light further

117
Q

what are concave lenses used for

A

correct short sightedness
as light is focused on the front of the retina so needs to be spread out slightly to be able to be focused onto the retina

118
Q

features of convex lenses

A

wider at the centre
focus light inwards
horizontal rays focus onto focal point

119
Q

what are convex lenses used for

A

magnifying glasses]
binoculars
correct long sightedness

120
Q

what do convex lenses do

A

focuses the rays closer

121
Q

magnification equation

A

image height / object height

122
Q

law of reflection

A

for a plane mirror the angle of incident is equal to the angle of reflection

123
Q

what does each colour within visible light spectrum have

A

its own narrow band of wavelength and frequency

124
Q

difference between blue and red

A

blue has a shorter wavelength and higher frequency than red

125
Q

what is sunlight in terms of its composition

A

a mix of all colours and this mix appears white (white light is normal light)

126
Q

types of reflection

A

specular
diffuse

127
Q

what is specular reflection

A

smooth surface gives a single reflection

128
Q

what is diffuse reflection

A

reflection off a rough surface causes scattering

129
Q

how do colour filters work

A

the filter absorbs every other colour and only lets a certain wavelength (colour) through

130
Q

what does an opaque object have

A

colour

131
Q

what is an opaque objects colour determined by

A

the strength of reflection for different wavelengths

132
Q

what happens to wavelengths that are not reflected

A

they are absorbed

133
Q

what happens if all wavelengths reflect

A

it is white in colour

134
Q

what happens if all wavelengths are absorbed

A

it appears black

135
Q

what does the wavelength absorbed equal

A

the colour which it appears

136
Q

what are objects that transmit light

A

either transparent or translucent (scatter most light and on;y let some through)

137
Q

what do all objects do

A

emit and absorb infrared radiation

138
Q

what happens the hotter the body

A

the greater amount for radiation released per second (more powerful)
the greater amount of shorter wavelength radiation released (waves with more energy like x rays)

139
Q

what is a black body

A

an object that absorbs all the radiation it receives and doesn’t transmit or reflect any
therefore it emits all types of radiation

140
Q

what does a body do at its constant temperare

A

it is still radiating / receiving radiation
but it is absorbing radiation at the same rate of emitting it

141
Q

what does a body do at an increasing temperature

A

absorbs more energy than it emits

142
Q

what does a body do when cooling down

A

energy is released at a greater rate than it absorbs

143
Q

what is the suns energy mostly absorbed by

A

the earths atmosphere , and some is reflected

144
Q

what does the amount for energy re radiated and absorbed lead to

A

the earths temperature

145
Q

process of the earth receiving solar radiation

A

solar radiation passes through the atmosphere
some solar radiation is reflected by the atmosphere and earths surface
about half is absorbed by earths surface
radiation converted to heat energy causing emission of ir radiation back into the atmosphere
some of the ir radiation is absorbed and reemitted by greenhouse gas molecules
some ir radiation passes through the atmosphere and into space

Physics (17 decks)

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