Waves 1 Flashcards
Waves in air, fluids and solids.
1
Q
What do waves do?
A
Waves transfer energy from one place to another without transferring matter.
2
Q
What are the two main types of wave?
A
-Transverse
-Longitudinal
3
Q
Give an example of a transverse wave.
A
-The ripples on a water surface.
-Light waves.
4
Q
What do longitudinal waves show?
A
Areas of compression and rarefaction.
5
Q
Give an example of a longitudinal wave.
A
Sound waves (travelling through air).
6
Q
Sometimes our brain can interpret the energy transferred by waves as what?
A
Meaningful information e.g. images from light waves.
7
Q
Longitudinal waves.
A
The particles in longitudinal waves have oscillations parallel to the direction of wave travel.
(think slinky)
8
Q
Transverse waves
A
The particles in transverse waves have oscillations perpendicular to the direction of wave travel.
(think Mexican wave)
9
Q
Explain what happens to the particles in a transverse wave. e.g. in a ripple.
A
The particles (e.g. of water) do not move along the wave.
Instead, each moves a short distance up and down, at right angles to the flow of energy which is from left to right.
10
Q
Describe the difference in how transverse and longitudinal waves are produced.
A
A transverse wave is produced when an object vibrates perpendicular (at 90°) to the direction of wave travel.
Whereas a longitudinal wave is produced when an object vibrates parallel to the direction of wave travel.
11
Q
In what ways are transverse and longitudinal waves different?
A
-They are produced differently
-The particles oscillate in different directions to each other (when compared to the direction of wave travel)
-Can have different speeds, frequencies, and wavelengths.
12
Q
Give two ways in which longitudinal and transverse waves are similar.
A
They both transfer energy without transferring matter and have an amplitude, speed, wavelength and frequency.
13
Q
Amplitude
A
The maximum displacement of a point
on a wave away from its rest position. (the x-axis).
14
Q
Wavelength
A
The distance from a point on one wave to the equivalent (identical) point on the adjacent wave.
(look for a complete vibration before repetition).
15
Q
Frequency (of a wave)
A
The number of waves passing a point
each second.
16
Q
What is the equation for frequency?
A
1 ÷ time for one full wave (period)
17
Q
What is λ the symbol for?
A
Wavelength
18
Q
What is the unit for wavelength?
A
metres, m
19
Q
What is the unit for frequency?
A
hertz, Hz
20
Q
What is the symbol for frequency?
A
f
21
Q
What is the name given to the time taken for one entire oscillation of a wave?
A
Time period.
22
Q
Symbol for time period. (or just ‘period’).
A
T
23
Q
Unite for time period. (or just ‘period’).
A
seconds, s
24
Q
What is the equation for (time) period?
A
period = 1 ÷ frequency
T = 1 ÷ f
25
What is wave speed?
The speed at which the energy is transferred (or the wave moves) through the medium.
26
For ripples on a water surface, what travels?
The wave, not the water itself.
27
For sound waves in air, what travels?
The wave, no the air itself.
28
Explain what happens to the particles in a longitudinal wave. e.g. in sound waves. .
The particles (e.g. of gas) do not move along the wave.
Instead, each moves only a short distance back and forth, parallel to the direction that the wave is travelling.
29
Compressions
Regions of high pressure where the particles of the wave are closer together than normal.
30
Rarefactions
Regions of low pressure where the particles of the wave are further apart than normal.
31
When asked to calculate the complete wave/wavelength, what must we do?
Count the extra bits! e.g. 3.75 waves
32
What do we call the top of a wave?
Crest/Peak
33
What do we call the bottom of a wave?
Trough
34
How do we represent waves?
Displacement- distance graphs (where distance is on the x-axis).
or
Displacement - time graphs (where period is on the x-axis).
35
What does displacement represent on a displacement - distance graph? (y-axis)
How far from the rest point the wave has oscillated.
36
What does distance represent on a displacement - distance graph? (x-axis)
How far the wave has travelled from its starting point.
37
What is THE wave equation?
wave speed = frequency × wavelength
38
What is the symbol equation for THE wave equation?
v = f λ
39
What is the unit for wave speed?
Metres per second, m/s
40
What is the symbol for wave speed?
v
41
Give an alternative way to calculate frequency (not 1/period)
Number of waves ÷ time (s)
42
What type of wave obeys the wave equation?
ALL waves.
43
Which format do scientists write answers in???
decimals
44
Which button on the calculator is veeery helpful with standard form?
ENGnotation (gives in factors of 10³)
45
What does G, giga, mean?
x 10⁹
46
What does M,mega mean?
x 10⁶
47
What does K, kilo mean?
x 10³
48
What does m, milli mean?
x 10⁻³
49
What does μ, micro,, mean?
x 10⁻⁶
50
What does n, nano, mean?
x 10⁻⁹
51
What can we do with prefixes?
Swap them for the powers of 10 they represent.
52
For calculations, (particularly with standard form) make sure you use...
brackets in your calculator!
53
Speed =
distance ÷ time
54
Distance =
speed x time
55
What is the symbol equation for speed = distance ÷ time?
v = s/t
56
What is the symbol for speed?
v
57
What is the symbol for distance?
s
58
What is the speed of sound in air?
330 m/s
59
What piece of equipment can we use to measure long distances?
Trundle wheel
60
Describe a source of error from the speed of sound in air practical that could explain why your value is less than the published value.
The reaction time of the person with the stopwatch.
If this is slow, it will increase the time measurements.
61
Suggest an improvement to the echo method that would give a more accurate value for the speed of sound.
Increase the distance from the wall so there is a greater time frame in which to measure time.
62
What is the most likely error in the speed of sound practical?
Human error - (slow) reaction time.
63
Describe a method to measure the speed of sound waves in air.
(using two microphones and an oscilloscope, steps 1 and 2)
-Set up two microphones one in front of the other at different distances from a loudspeaker
-Set the frequency of the sound from the loudspeaker to a known, audible value
64
Describe a method to measure the speed of sound waves in air.
(echo method)
-Measure the distance from the source of the sound (e.g. a partner clapping) to the reflecting surface (a wall)
-Measure the time interval between the original sound being produced and the echo being heard (using a stopwatch)
-Use the equation speed (m/s) = distance (m) ÷ time (s) to calculate the speed of sound in air.
-Repeat the experiment a number of times over a range of distances to obtain accurate results.
65
If using the echo method, when calculating wave speed, what MUST we do?
Double the distance (as the wave travels to the wall AND back!)
66
How could we remove human error in the speed of sound wave practical?
Use an oscilloscope.
Use a signal generator, speaker, and two microphones with an oscilloscope in the middle of the two. (simple diagram).
67
Describe a method to measure the speed of sound waves in air.
(using two microphones and an oscilloscope, steps 3, 4, and 5)
-Display the two waveforms on the oscilloscope. Measure the distance between the microphones.
-Move the microphones apart so that the waveforms move apart by 1 wavelength
-Calculate the speed of sound using the equation wave speed (m/s) = frequency (Hz) x wavelength (m)
68
Describe a method to measure the speed of ripples on a water surface.
(steps 1 and 2)
-Get a ripple tank and set the power supply to vibrate the paddle at a low frequency
-Place white card beneath the tank on which the water will create shadows (darker at peaks, lighter at troughs)
69
Describe a method to measure the speed of ripples on a water surface.
(steps 3, 4, and 5)
-Use a strobe light to 'freeze' the water waves so you can measure the wavelength
-Count the number of waves that pass a point in 10 seconds and divide by 10 to get a mean frequency
-Use the equation v = fλ to calculate the speed of the water waves
70
Explain how you could obtain a value for the speed of sound in air with a small percentage error. (4)
Speed of sound in air is found by measuring a distance for the wave to travel and the time over which the distance is covered.
Having a large distance and a large time for these measurements, and using equipment with a high degree of accuracy, will lead to a small percentage error.
71
Describe the relationship between frequency and wavelength.
There is an inversely proportional relationship between frequency and wavelength.
As frequency increases, wavelength decreases in proportion.
Hence, wave speed stays constant when waves travel through a medium (e.g. sound).
72
What causes a 'standing' wave?
(not on spec but useful!!!)
One wave travels along a string
It bounces off the pulley
A wave bounces back and travels in the other direction
The two waves 'interfere' with each other, causing a standing/stationary wave.
73
What three things can happen to waves at the boundary between two different materials/mediums?
-Reflected
-Absorbed
-Transmitted
74
What happens when a wave is absorbed by a material?
The wave is taken in by a body but does not pass through it.
Energy from the wave is transferred to that material's energy stores.
75
What happens when a wave is transmitted?
The wave passes through a body.
(Often leads to refraction)
76
Reflection
The wave 'bounces' off the boundary between two materials.
77
What does 'the boundary between two materials' look like?
A surface.
78
Give an example of waves being transmitted.
Radio waves can pass through walls and be detected by a radio receiver.
79
Give an example of waves being absorbed.
Micro waves are absorbed by food in a microwave oven.
80
State the law of refraction
The angle of incidence equals the angle of reflection.
81
When constructing ray diagrams, what must we use for the angles?
A protractor!
This includes accurately drawing the normal at 90° to the boundary.
82
What is a 'normal'?
A line at 90° to the surface where a light ray hits it.
It should meet the point of incidence.
83
What types of waves can be reflected at a surface?
Light waves, water waves, and sound waves.
84
Angle of Incidence
The angle we measure for a ray hitting a mirror (from the normal).
85
Angle of Reflection
Opposite the angle of incidence and equal in size to it (measured from the normal).
86
What is the name for the wave approaching a surface?
Incident ray
87
What is the name for a wave's reflection off of a surface?
Reflected ray
88
How do we draw a plane mirror?
A straight line with diagonal lines from it on the non-shiny (hairy) side.
89
How do we draw a normal?
As a dotted line perpendicular to the surface.
90
When a wave meets the boundary between two materials, what happens to it depends on what?
-The wavelength of the wave
-The properties of the two materials
91
What is a virtual ray?
Where a ray appears to travel from.
(e.g. it may seem to come from behind a mirror).
92
What is a virtual image?
When an object appears to be within a mirror (or some other reflective surface).
93
Where does a virtual image appear to be?
Opposite the actual object.
(Because it's achieved at the point where virtual rays go from converging to diverging.)
94
If the angle of incidence was 45°, what would the angle of reflection be?
45°
95
What is the point of incidence?
The exact place where a ray hits the boundary between two different materials.
96
What is specular reflection?
When the boundary between two materials is flat all normals are in the same direction.
This means that all light rays are reflected in the same direction, giving a clear image.
(allowing you to see yourself in the surface).
97
What is diffuse (scattered) reflection?
When the boundary between two materials isn't flat so normals (which are always 90° to the surface) will be in different directions.
This means that light rays get scattered in different directions.
This means that you cannot see yourself in the surface.
98
What is refraction?
The change in direction of a wave when it crosses a boundary between two transparent materials.
This is caused by a change in speed.
99
What happens when a ray of light is moving along the normal so meets a surface at 90°?
They continue to travel through the material without a change in direction.
100
What four things can waves be?
Reflected, refracted, transmitted or absorbed.
101
Explain why you can get sunburnt when you are outside on a sunny day.
You'll get sunburnt be absorbing ultraviolet light which is transmitted by the atmosphere and absorbed by skin.
102
Suggest how the absorption of different wavelengths of infrared radiation by molecules in the atmosphere is useful.
It stops infrared radiation reaching us which could cause overheating.
103
Suggest how the absorption of different wavelengths of infrared radiation by molecules in the atmosphere is a problem.
Stops infrared radiation getting to us from space which could help us to detect other objects in space.
May have an impact on studies of the atmosphere e.g. meteorology.
104
Why can't you get sunburnt inside?
Ultraviolet light isn't transmitted by concrete walls so cannot be absorbed by your skin when you are indoors.
105
When drawing ray diagrams for virtual rays, what must we do?
Draw your plane mirror and a normal to this with the 90° angle
-Draw two reflection lines from the object (equal angles going in and out from plane mirror/surface
-Draw eyes and arrows on the real rays
-Use dotted lines for virtual rays
-Find where they cross
106
What happens to light rays when they travel into a more optically dense material?
They are refracted towards the normal (more).
This is because the light rays are travelling more slowly.
107
What happens to light rays when they travel into a less optically dense material?
They are refracted away from the normal (less).
This is because the light rays are travelling more quickly.
108
How do we cheat when drawing a ray diagram for a viral image?
By drawing in the virtual image exactly opposite the object (using a ruler to measure the same distance either side of the surface) straight away!
109
For virtual images, the distance from the real object to the mirror = ?
Distance inside mirror
110
What does the amount of change in direction of a wave when it's refracted depend on?
The difference in materials.
If the material is more optically dense, the wave slows down more and so is refracted more.
111
Order these in terms of least to most optically dense:
glass, water, air, diamond
-air
-water
-glass
-diamond
112
When can waves be refracted?
ONLY when they approach the different media/material AT AN ANGLE.
113
Why do infrared rays not go past a wall?
They are absorbed/not transmitted by the wall.
They can also be reflected.
114
What is the normal hearing range for a human?
20 to 20,000 Hz.
115
Ultrasound
Sound waves with a frequency of above 20,000 Hz, and are therefore above the normal human hearing range.
116
Why can't sound travel in a vacuum?
There are no particles to vibrate.
117
Waves travel at different speeds in...?
different materials/mediums
118
Why do waves travel at different speeds in different mediums?
Different mediums have different densities.
119
What is the emergent ray?
The ray that is travelling out of a material, when it's previously been refracted.
120
The frequency of a wave...
...always stays the same!
121
What must happen to wavelength as a wave passes from one medium to another?
It increases/decreases because the speed of the wave increases/decreases.
This is due to the wave speed equation v = f λ and the frequency of a wave always stays the same.
122
Different wavelengths of light are refracted by...
...different amounts.
This means that if you put white light (containing all the wavelengths of visible light) through a triangular prism, the different colours will be refracted to different degrees.
This means they spread out like a rainbow.
123
If wave speed decreases, the wavelength of the wave...
decreases.
124
Fore electromagnetic waves like light, the denser the material...
...the slower the wave will travel through it.
125
For sound waves, the denser the material...
...the faster the wave will travel through it.
126
Why is human hearing limited?
The conversion of sound waves to solids works over a limited frequency range.
127
What are sound waves?
Vibrations that pass through the molecules of a medium.
128
What in the ear causes the sensation of sound?
Sound waves causing the ear drum and other parts to vibrate.
129
Why does human hearing range decrease with age?
Due to wear and tear of the cochlea and the auditory nerve, alongside damage from very loud sounds.
130
20,000 Hz is equal to what?
20 kHz
131
Why is a wavelength long in higher density mediums? (sound)
Sound waves speeds up in higher density mediums, which means that wavelength must be longer due to the equation v = f λ.
The frequency of waves does not change!
132
Why is a wavelength short in lower density mediums? (sound)
Sound waves slow down in lower density mediums, which means that wavelength must be shorter due to the equation v = f λ.
The frequency of waves does not change!
133
What type of wave is a sound wave?
Longitudinal
134
Describe the processes in the ear which allow us to hear.
-Once in the ear, sound waves travel across the ear canal
-They hit the ear drum, causing it to vibrate
-The vibrations are transmitted through the ossicles and the semi-circular canals into the cochlea
-The cochlea converts the vibrations into electrical signals and these get sent along the auditory nerve to your brain
-Your brain interprets the signals as sounds
135
How does the brain interpret electrical signals from the auditory nerve with high frequencies?
High- pitched sounds
136
How does the brain interpret intense electrical signals from the auditory nerve?
Louder sounds
137
How do sound waves travel through solid materials?
Sound waves travel as a series of compressions and rarefactions.
So, when they hit a solid, this causes particles inside the solid to vibrate.
These vibrating particles collide with their neighbours and pass on the vibrations.
This repeatedly happens, transmitting the sound wave through the material .
138
What gives us echoes?
When sound waves are refracted by hard, flat surfaces.
139
What three things can sound waves be?
-Reflected
-Transmitted (and hence refracted)
-Absorbed
140
For sound waves, the more densely packed the particles are in a medium...
...the more frequent collisions are between particles...
....so the more quickly vibrations are passed between them...
...so the faster the sound travels.
141
Does sound travel faster in solids, liquids or gases?
Solids.
(Solids>Liquids>Gases).
142
In what form do sound waves travel through the ear?
Vibrations
143
A soft sound (like a whisper) generates _______ vibrations.
smaller
144
Explain how a vibration becomes a sound that is heard.
An object vibrates, pushing air molecules into a series of compressions and rarefactions that are transmitted as a pressure wave.
145
Give an example of the production of a sound wave.
The vibration of a guitar string to produce a musical note.
The length, thickness, and material of the string determine the frequency of the note.
146
The frequency of the vibration of a solid is the same as what?
The frequency of the sound wave that is causing it to vibrate.
147
Why can humans only hear sounds in a limited frequency range?
Solids cannot be made to vibrate by every frequency of a wave.
So, the eardrum will not vibrate if the frequency is less than 20Hz or more than 20 kHz
148
Explain why sound waves are described in terms of their frequencies rather than their wave speed.
Sound waves have the same frequencies as the waves that cause them and this doesn't change when a sound wave passes from one material into another, whereas wave speed does change in different materials.
149
Name the types of wave used in detection of objects and the exploration of the body or Earth.
-Ultrasound
-Seismic waves
150
What is the use of waves based on?
-How they change velocity (speed) in different mediums
-Absorption (how much energy a wave loses as it travels through a material)
-Reflection
151
Ultrasound waves are _________ reflected when they ___________. This is due to ________.
partially
meet the boundary between two different media.
a change in density.
152
Describe how ultrasound waves can be used to produce an image of a foetus (4) [Pre-natal scanning]
Ultrasound waves are sent into the body from a transmitter.
They are reflected at the boundary between materials of different density e.g. blood and bone.
The reflected ultrasound is then detected by a receiver.
An image is produced on a computer monitor based on the information from the reflected ultrasound.
153
Explain how ultrasound can be used to determine the size and location of a crack inside a pipe (or any other solid product).
Ultrasound is reflected at the boundary between two materials of different densities.
When the ultrasound passes from the metal to the crack (which is air and has a lower density) it will be reflected.
The crack's position can be calculated using speed = distance x time.
154
The time taken for ultrasound reflections to reach a detector can be used to determine what?
How far away the boundary between two different media is.
This allows ultrasound waves to be
used for both medical and industrial imaging.
155
Why do bats naturally produce ultrasound?
-echo - location
-communication
156
Name the processes ultrasound can be used in.
-Medical scanning (including pre-natal-to check a foetus is healthy)
-Industrial imaging for quality checking (if there are any faults/cracks waves will be reflected at different places than expected)
-Sonar (echo-sounding )
157
What is echo- sounding (sonar)?
Using high frequency sound waves to detect objects in deep water and measure water depth.
(distance = speed x time)
158
In echo-sounding/sonar, where are the ultrasound waves fired from?
Boats/submarines to the sea floor.
159
How are seismic waves produced?
By earthquakes.
160
What are the two main types of seismic wave?
P- waves (longitudinal seismic waves)
S-waves (transverse seismic waves)
161
Differences between P-waves and S-waves.
P-waves are longitudinal, whereas S-waves are transverse.
P- waves are faster than S-waves.
P-waves can travel through solids and liquids, but S-waves cannot travel through liquids.
162
When do P-waves travel at different speeds?
Through solids vs liquids.
163
What do P and S waves provide evidence for?
The structure and size of the Earth’s core.
164
The study of seismic waves provided
new evidence that led to what?
Discoveries about parts of the Earth which are not directly observable.
165
What must we do when calculating depth using sonar pulses/waves?
Divide the distance by 2!
(because the wave has to go there and back but we only want to calculate the distance there)
166
Explain how the behaviour of P-waves and S-waves allowed scientists to determine the internal structure of the Earth.
By measuring which type of wave could be detected from different places around the Earth.
Scientists know that P-waves will travel through both solids and liquids.
P-waves can therefore be detected from one side of the Earth directly across to the other side. (using seismometers).
S-waves cannot be detected from one side of the Earth directly across to the other.
Scientists know they will not travel through liquids, so there must be a liquid outer core where they cannot get through.
The mantle must be solid.
167
What can seismic waves be?
-Reflected
-Refracted
-Absorbed
168
Why are seismic waves refracted?
Due to changes in density both between the different layers of the Earth and within them.
(Particularly within the mantle where constant refraction created the illusion that the waves are curving round - this is why certain areas don't get hit by earthquakes).
169
Why does a beam of white light turn into a rainbow when travelling into a glass prism?
White light waves travel from a less dense medium (air), into a more dense medium (glass).
As this happens, the different wavelengths of light contained within the white light have all refracted at different angles (so the colours spread out).
170
What is the wave speed of radiowaves in air equivalent to?
The speed of light.
171
speed of water waves?
5 m/s
172
Speed of light
3 x 10⁸ m/s
173
Speed of an S-wave
4000 m/s
174
Amplitude (KO)
Height from centre line
175
Wavelength (KO)
The distance from peak to peak
176
Frequency (KO)
The number of waves passing a point each second
177
Period (KO)
The time for one wave to pass a given point
178
Oscillation (KO)
Movement back and forth
179
Transverse wave (KO)
Oscillations are perpendicular to the direction of energy transfer (e.g. EM wave, ripples on water)
180
Longitudinal wave (KO)
Oscillations are parallel to the direction of energy transfer (e.g. sound).
Show areas of compression and rarefaction (spread out)
181
Wave (KO)
Transfer of energy with no transfer of particles
182
When would direction not change when a wave hits a surface?
When the wave travels perpendicular to the normal.
183
List waves that can be refracted.
-Sound waves
-Water waves
-Light waves
184
In what medium do sound waves travel more quickly?
Warm, less dense air.
They travel more slowly in cooler, denser air.
(they can change direction)
185
In what medium do water waves travel more quickly?
They travel more quickly in deep water than in shallow water.
(they can change direction)
186
In what medium do light waves travel more quickly?
Air.
They travel more slowly in glass = bend towards the normal
187
How do humans produce ultrasound?
Using electrical devices to produce electrical oscillations which are converted into ultrasound waves.
188
What is ultrasound?
Sound with frequencies above human hearing (above 20,000 Hz)
189
How can seismic waves be detected?
Using seismometers.
