Waves Flashcards
(185 cards)
1
Q
What happens when waves travel through a medium?
A
Particles of the medium oscillate and transfer energy between each other, overall the particles stay in the same place as only energy is transferred
2
Q
What is the amplitude of a wave?
A
Maximum displacement of a point on the wave from its undisturbed position.
3
Q
What is wavelength?
A
Distance between same point on two adjacent waves for example between trough of one wave on the trough of the wave next to it)
4
Q
What is frequency?
A
Number of complete waves passing a certain point per second.
5
Q
What is frequency measured in?
A
In Hertz Hz 1 Hz is one wave per second
6
Q
From the freuqency what can you find?
A
The period of a wave. This is the amount of time it takes for a full cycle of the wave.
7
Q
How to calculate the period of a wave.
A
T = 1/f t= period (s) F= frequency Hz
8
Q
Describe a transverse wave
A
Oscillations (vibrations are perpendicula to direction of energy transfer
9
Q
Give examples of transverse waves
A
1= all electromagnetic waves like light 2= ripples and waves in water 3= a wave on a string
10
Q
On a graph what does amplitude look like?
A
From x axis to peak
11
Q
On a graph what does wavelength look like?
A
Line between peaks
12
Q
On a graph what does a crest look like?
A
The peak
13
Q
On a graph what does undistrubed position look like?
A
A straight line
14
Q
Give examples of mechanical waves
A
Water waves Shock waves Waves in springs ropes
15
Q
Describe longitudinal waves
A
oscillations are parallel to direction of energy transfer.
16
Q
Examples of longitudinal waves.
A
Sound waves in air like ultra sound shock waves likes some seismic waves
17
Q
What is wave speed?
A
Speed at which energy is being transferred or the speed the wave moves at
18
Q
Give the equation for wave speed
A
v = f x wavelength V= wavespeed in m/s F= hz Wavelength symbol upside down y = m
19
Q
How to measure the speed of sound using an oscillioscope?
A
- Set up oscillioscope so the detected waves at each microphone are shon as seperate waves.
- Start with both microphones next to the speaker then slowly move one away until the two waves are aligned on the display but have moved on wavelength apart.
- Measure distance between microphones to find one wavelength.
- Use forumula v=fxwavlength to find speed of sound waves passing through air.
- The frequency is whatever you set signal generator to but around 1khz Speed of sound is around 330 m/s
20
Q
How to measure the speed of water ripples through a lamp?
A
- Using a single generator attatched to the dipper of a ripple tank create water waves at a set frequency
- Use a lamp to see wave crests on a screen below the tank.
- Make sure size of waves shadows are the same size as the waves
- Dsitance between each shadow line is equal to one wavelength.
- Measure distance between shadow lines that are 10 wavelengths apart then divide distance by 10 to find average wavlength.
- If you struggle to measure distance take a photo fo shadows and ruler and find wavelength from photo
- use v=fλ to calculate waves speed of waves.
- This set up allows you to measure wavelenght without diturbing waves.
21
Q
Describe experiment for how to use wave equation fro waves on strings.
A
- Turn on signal generator and vibration transducer.
- The string will start to vibrate
- Adjust frequency of signal generator until there is a clear wave on string.
- The frequency needed depends on length of string between pulley and transducer and the masses you have used.
- Measure wavelength of these waves
- To do this measure 4-5 half wavelenghts or as many as you can in one go, divide to get mean half wavelength then double this mean to get full wavelength.
- Frequency of wave is whatever the signal generator is set to.
- find wave speed with the formula v=fλ
22
Q
When waves arrive at a boundary between two different materials what three things can happen?
A
- The waves are absorbed by the material the wave is trying to cross into this transfers energy to materials energy stores
- Waves are transmitted which means the waves carry on travelling through the new material.- this leads to refraction.
- Waves are reflected.
- Depends on wavelength of the wave and properties of materials involved.
23
Q
What does the angle of incidence equal?
A
The angle of refelection
24
Q
What is the angle of incidence?
A
Angle between the incoming wave and the normal
(to tell it is the incoming ray with the arrow going inwards)
25
What is the angle of reflection?
Angle between the reflected wave and the normal.
(to tell it is the angle with an arrow pointing outwards)
26
What is the normal?
An imaginary line that is perpendicular (at right angles) to the surface at the point of incidence (where the wave hits the boundary)
27
What is the point of incidence?
Point where the wave hits the boundary.
28
When does specular reflection happen?
Wave is reflected in a single direction by a smooth surface
eg: light is reflected by a mirror you get a clear reflection
29
What is diffuse reflection?
When a wave is reflected by a rough surface eg:lots of paper and the reflected rays are scattered in lots of different directions.
30
When does diffuse reflection happen?
The normal is different for each incoming ray so angle of incidence is different for each ray too.
The rule angle of incidence = angle of reflection still applies.
31
What happens when light is reflected by a rough surface?
Surface is matte not shiny and you don't get a clear reflection of objects.
This is diffuse reflection.
32
What type fo wave are electromagnetic waves?
Transverse waves, transfer energy from a source to absorber.
eg: hot object transfers energy by emmiting infared radiation which is absorbed by surrounding air.
33
How do all EM waves travel?
At the same speed through air or a vaccum (space)
34
What do electromagnetic waves form?
A continuos spectrum over a range of frequencies
They are grouped in seven basic types based on wavelength and freqency
35
Name the seven waves in the continuos spectrum
Raw= radio waves
Meat= microwaves
Is= infra red
Very= visible light
Unsanitary= Ultra violet
eXcept = X-Rays
Giraffe= Gamma rays
36
From the continuos spectrum describe which wha has highest frequency amd what has the lowest.
Radio waves - Gamma rays is low to high frequency
Radio waves - Gamma rays is long wavelength to short wavelength
37
In the continuos spectrum why is there a large range of frequecnies?
EM waves are generated by a variety of changes in atoms and their nucleus.
this explains why atoms can absorb a range of frequencies so each one causes a change.
38
Why do EM waves have a lot of purposes?
Because they have a lot of different properties.
39
Define the term refraction.
When a wave crosses a boundary between materials at an angle and changes direction
40
What does how much a wave refract depend on?
How much the waves speeds up or slows down.
Depends on density of two materials the higher the density the slower a wave travels through it.
41
What happens if a wave crosses a boundary and slows down?
It bends towards the normal.
But if it crosses into a material and speeds up it bends away from the normal.
42
What happens to the wavelength of a wave when it refracts?
It changes, but the frequency stays the same.
43
What happens if the wave travels along the normal?
It does change speed but doesnt refract as it doesn't change direction
44
What does the wave fronts being closer together show?
change in wavelength and a change in velocity
45
What is the optical density of a material?
Measure of how quickly light can travel through a material.
Higher optical density the slower light waves travel through it.
46
How to draw a ray diagram for a refracted light ray?
Draw boundary between two materials
Draw a normal line in middle
Draw the incident ray which meets the normal or if given draw it according
Now draw refracted ray on other side
Is second material is denser than first then refracted ray bends more to the normal so it is smaller than angle of incidence
If second material is less optically dense angle of refraction is larger than angle of incidence
47
When doing experiments with rays of light what conditions should the room be?
dim room so you can clearly see light rays
Both use ray box or lasers to produce thin ray of light so you can easily see middle of ray when tracing and measuring angles from it
48
How to use transparent materials to investigate refraction?
Boundaries between different substances refract light by different amounts
1= place transparent rectangular block on a piece of paper and trace around it.
2= use ray box or laser to shine a ray of light at middle of one side of the block
3= Trace incident ray and mark where light ray emerges on the other side of block
4= remove block and with straight line join incident ray and emerging point to show path of refracted ray through block.
5= draw normal at pont where light ray enter block
6= Use protactor to measure angle between incident ray and the normal
7= and angle betwen reflected ray and hte normal which is the angle of refraction
8= repeat experiment with rectangular blocks made of different material keeping incident angle same throughout.
49
Why does angle of refraction change for different materials?
Due to different optical densities
50
give the experiment for how light is reflected by different materials.
1= take a piece of paper and draw straight line across it
2= place an object so one of its sides lines up with the line you drew
3= Shine ray of light at object's surface and trace incoming and reflected light beams
4= Draw normal at the point where ray hits the object
5= use a protractor to measure angle of incidence and angle of reflection and record values in table
6= Make note of width and brightness of reflected light ray
7= repeat experiment for range of objects
51
What do smooth surface like mirrors give?
Clear reflections
Reflected ray is as thin and bright as incident ray
52
What reflections do rough surfaces like paper cause?
Diffuse reflection
Casues reflected beam to be wider and dimmer or not observable
53
What are EM waves made up of?
Oscillating electric and magnetic field.
54
What are alternating current made up from
oscillating charges
As charge oscillates they produce oscillating electric and magnetic fields ie:electromagnetic waves
55
What is the frequency of waves produced equal to?
Frequency of the alternating current
56
How do you produce radio waves?
Alternating current in an electrical circuit.
## Footnote
Object in which electrons oscilliate to create the radio waves.
When transmitted radio waves reach a reciever the radio waves are absorbed
Energy carried by the waves is transferred to the electrons in the material of a reciever.
Energy causes electrons to oscilliate and if reciever is part of complete electrical circuit it generate ac
This current has same frequency as radio wave that generated it
57
What is a transmitter?
Object in which electrons oscilliate to create the radio waves.
58
What are radio waves?
EM radiation with wavelengths longer than 10cm
59
How long are long wave radios?
1-10km
transmitted from london and recieved half way around world.
60
Why can long wave radios be recieved from far distances?
They diffract (bend) around the curved surface of Earth.
They also diffract around hills into tunnels etc
Makes it possible radio signals to be recieved at long distances from transmitters
61
How long are short wave radio signals?
10m-100m
like long wave can be recieved at long distance from transmitter
As they are reflected from the ionsphere which is electrically charged layer of the earth upper athmoshphere.
62
What wave does bluetooth use?
Short wave radio waves
To send data over short distances between devices without wires so you can use phone whilst driving.
63
What are medium wave signals?
They reflect from ionsphere depending on athmosheric conditions at the time of day.
64
What radio waves are used in TV and FM radio?
short wavelenghts.
To get reception must be in direct sight of transmitter, signal does not bend or travel through buildings.
65
What does communication to and from satelites use?
Microwaves which can easily pass through earths watery athmosphere
66
How does a satellite TV work?
* Signal from transmitter is transmitted to space
* Picked up by satallite reciever dish orbiting thousands of km above Earth.
* Satellite transmits signal back to Eath in a different direction.
* Where it is received by satellite dish on ground
* Slight time delay between signal sent and recieved as long distance it needs to travel
67
In communication what do the microwaves need to pass through?
The Earths watery athmosphere
68
In microwave ovens what do microwaves need to be absorbed by?
* Water molecules in food. So they use different wavelength to those used in satellite communications.
* Microwaves penetrate up to a few cm into the food being absorbed and transferring the energy they are carrying to water molecules in food causing water to heat up.
* Water molecules then transfer this energy to rest of molecules in food by heating which cooks food quickly
69
What is infared radiation?
it is given out by all hot objects and the hotter the object the more infared radiation it gives out
70
What are infared cameras for?
Detect infared radiation and monitor temperature.
71
How do infared cameras work?
camera detects IR radiation turns it into an electrical signal, which is displayed on as a screen as a picture.
The hotter an object is the brighter it appears.
72
What causes objects to become hotter?
Absorbing IR radiation
73
What can be cooked using Infrared Radiation
Food, temp of food increases when absorbs IR
eg:toasters heating elements
74
How do electric heaters heat a room?
- long peice of wire that heats up when current flows through it
- Wire emits lots of infrared radiation an visible light as wire glows
- Emmited IR radiation absorbed by objects and air in room
- Energy transferrred by IR waves to thermal energy stores of objects cause temp to increase
75
What are optical fibres?
Thin glass or plastic fibres that can carry data from telephones or computers over long distances as pulses of visible light.
76
Why do optical fibres work?
Because of reflection light rays are bounced back and forth until they reach the end of the fibre.
Visible light is used in optical fibres.
Light is not easily absorbed or scattered as it travels along a fibre
77
What if flourescence?
Property of certain chemicals where UV radiation is absorbed and then visible light is emmited.
That is why they look so bright beacuse they emit light
78
What do flourescent lights generate?
UV radiation which is absorbed and re-emmited as visible light by a layer of phosphorus on the inside of the bulb.
79
Advantages of flourescent light
They are enrergy efficient so good to use when light is needed for a long time like in schools
Flourescent lights only emit small amount of UV radiation so are not harmful
80
What is ultraviolet radiation produced by?
The sun, and exposure gives people sun tan etc
81
What to people do when it is not sunny?
Go to tanning salons where UV lamps are used to give them artifical suntan
But overexposure to UV radiation can be dangerous
82
What does a radio grapher do?
They take X-Rays photographs of people to see if they have broken bones,
83
What gives you a X-Ray image?
Pass easily through flesh but not easily through denser materials like bones or metal.
So it is the amount of radiation absorbed/ not absorbed that gives you the X-Ray image
84
What do radiographers use?
X-rays and gamma rays to treat people with cancer (radiotherapy)
85
Why do radiographers use x-rays and gamma rays to treeat cancer?
High does of these rays kill all living cells so they are carefully directed towards cancer cells to avoid killing healthy cells
86
What else can gamma radiation be used for?
* Medical tracer
* Where a gamma emmiting source is injected into the body and its progress is followed around the body.
* Gamma radiation is well suited to this as it can pass out through the body to be detected.
87
What do radiographers wear when using X-rays and gamma rays?
Lead apron and stand behind lead screen or leave room to keep exposure to them minimum
88
What are the effects of each type of radiation?
How much energy the wave transfers
89
How much energy do low frequency waves transfer?
Radio Waves
Dont transfer much energy
Mostly pass through soft tissue without being absorbed
90
How much energy do high frequency waves transfer?
Like UV rays, gamma rays, X rays
Transfer lots of energy so cause lots of damage
91
What does UV damage?
Surface cells, lead to sunburn and causes skin to age preamturely
Serious effects are blindness and risk of skin cancer
92
What type of radiation are gamma and x rays?
Ionising radiation
Carry enough energy to knock of electrons of atoms
Casue gene mutation or cell destruction and cancer
93
Give an example of how UV xrays and gamma rays outweigh the negatives
Risk of person involved in car accident developing cancer from having X ray photograph taken is much smaller than potential health risk of not finding and treating injuries
94
What is radiation dose?
A meausure of risk of harm from the body being exposed to radiation is
measured in sieverts
95
What does the risk of radiation depend on?
Total amount of radiation absorbed and how harmful the type of radiation is.
96
How many milli sieverts is one sievert?
1000mSv= 1Sv
97
What does a CT scan use?
X-Rays and a computer to build up a picture of inside of a patients body
98
What happens when a patient has a CT scan on their chest?
4 times more likely to suffer from damage to genes than if they had a head scan
99
How do lenses form images?
By refracting light and changing its direction.
100
Name the two main types of lens
Convex
Concave
101
Desribe a convex lens
Bulges outwards
Causes rays of light parallel to axis to to converge (come together) at the prinicipal focus point
102
Describe a concave lens
Caves inwards
Causes parallel rays of light to diverge (spread out)
103
What is the principal focus of a convex lens?
Where rays hitting the lens parallel to axis all meet
104
What is the principal focus of a concave lens
Point where rays hitting the lens parallel to the axis appear to all come from you can trace them back till they meet up at a point behind lens
105
What is the focal length?
Distance from centre of lens to principal focus
106
What are the three rules for refraction in a convex lens
1= incident ray parallel to axis refracts through lens and passes through principal focus onto other side
2= incident ray passing through principal focus refracts through lens and travels parallel to axis
3= incident ray passing through centre of lens carrieds on in same direction
107
Three rules for refraction in a concave length
1= incident ray parallel to axis refracts through lens and travels in line with principal focus so it appears to have come from principal focus
2= inciden ray passing through the lens towards principal focus refracts through the lens and travels parallel to axis
3= incident ray passing through the centre of lens carries on in same direction
108
What is a real image?
Where light from an object comes together to form an image on a screen like image formed on eyes retina
109
What is a virtual image?
When rays are diverging.
So light from object appears to be coming from a completely different place.
110
When you look in a mirror what image do you see?
A virtual image of your face
As the objects appears to behind the mirror
111
How can you get a virtual image?
When looking at an object through a magnifying glass
The virtual image looks bigger than the object really is
112
How to describe an image properly
1= how big it is compared to the object
2= upright or inverted relative to the object
3= whether it is real or virtual
113
How to draw a ray diagram for an image through a convex lens
1= pick a point on top of an object
2= draw a ray from object to lens as in the middle
3= draw another ray from top of image going through the middle lens
4= The incident ray is refracted through the principal focus
5= the ray pasing middle doesn't bend
6= mark where rays meet that ehy top of the image
7= repeat process for point on bottom of object so when the bottom of an object is on a axis the bottom of an image is also on a axis
114
What does the image look like if the object is more than 2 focal lengths away from the image?
Image is diminshed (smaller)
Image is inverted
Image is real
115
What does the image look like if the object is one to two focal lengths away from the image?
Image is magnified
Image is inverted
Image is real
116
What does the image look like if the object is nearer than one focal lengths away from the image?
Virtual image
Upright
Magnified / Bigger than the object
117
How to draw a ray diagram for a concave lens?
1= pick a point on top of object
2= draw ray going from top of object parralel to axis of lens so in middle
3= draw another line from top crossing middle
4= The incident ray that is parallel to axis is refracted so appears to have come from prinicpal focus.
5= draw ray from principal focus make it dotted berfore it reaches lens
6= mark where refracted lens meets that is top of image
118
Describe the image of a concave lens
Always produces a virtual image.
Image is right way up
Smaller than the object
Same side of the lense as the object
119
How do magnifying glasses work?
Work by creating a mangified virtual imag.e
Object being magnified must be closer to lens than focal length
Image produced is virtual so light rays do not come from the place where the image appears to be.
120
What is the magnification formula?
Magnification = image height /object height
magnification of a ratio so no units
As long as units are same you can meausure height in whatever unit you want.
121
Give the magnification triangle
i
A x M
AKA= I am triangle
122
What is the visible light spectrum?
Range of wavelengths we percieve as different colours.
123
What does each colou of the visual light spectrum have?
narrow range of wavlengths and frequencies.
Ranging from violets at 400nm to red at 700nm
124
How do colours make other colours?
They mix
125
What are the only colours you can't make by mixing?
Red
Green
Blue
126
What happens when all the different colours are put together?
The create a white light
127
What do opaque objects to do light?
They do not transmit light.
When visible light waves hit them they absorb some wavelengths of light and reflect others
128
What does the colour of an opaqe object depend on?
Which wavelengths of light are most strongly reflected.
Eg: red apple appears to be red as wavelengths corresponding to the red part of the visible spectrum are most strongly reflected. Other wavelengths of light are absorbed
129
What do opaque objects that are not a primary colour reflect?
Wavlelengths of light corresponding that colour
OR
Wavelengths of primary colours that mixed to make that colour.
130
Waht do white objects reflect?
All the wavelengths of visible light equally
131
What do black objects do to wavlengths?
Absorb all wavelengths of visible light.
Eyes see black as the lack fo any visible light
132
What do transparent (see through) and translucent (partialy see through) objects do to light?
They transmit it
so not all light that hits the surface of the object is absorbed or reflected some can pass through
133
What is a transparent/translucent objects colour related to?
Wavelengths of light transmitted and reflected by it
134
Why are colour filters used?
To filter out different wavlengths of light so only certain colours arr transmitted and the rest are absorbed.
135
What does a primary colour filter do?
Only transmits that colour
so if white light is shone at a blue colour filter only blue light is let through rest of light is absorbed.
136
If you look at a blue obect through a blue filter paper what do you see?
It will still look blue
Blue light is reflected from objects surface and is transmitted by the filter
137
In a primary colour filter what happens if the object is a different colour to the light?
Object appear as black when viewed through the filter.
All light reflected by object is absorbed by the filter.
138
What do filters that are not for primary colours do?
Let through both wavelengths of light for that colour and wavelengths of primary colours that can be added together to make that colour.
139
What do all objects continually emit and absorb?
Infrared Radiation
140
Where is infrared radiation emmited from?
The surface of an object
141
What does a hotter object radiate?
More infrared radiation in a given time
142
What does an object hotter than its surrounding like a cup of tea on a table do?
Emits more IR radiation than it absorbs as it cools down.
143
What does an object that is cooler than its surroundings do?
Absorbs more IR radiation, than it emits as it warms up
144
What to objects at a constant temperature do?
Emits infrared radiation at same rate that they are absorbing it.
145
What is a black surface better than a white surface?
Black better at absorbing and emmiting radiation then a white one.
Matte surface is better at absorbing and emitting radiation than a shiny one.
146
What is a leslie cube?
Hollow watertight metal cube made of metal like aluminum.
4 vertical faces have different surfaces lke matte black paint, matte white paint, shiny metal, dull metal
147
What does a leslie cube investigate?
IR emmisions by different surfaces
148
Describe the experiment for investigating IR emmision by different surfaces with a leslie cube
1= place empty leslie cube on heat proof mat
2=boil water in a kettle and fill leslie cube with boiling water
3= Wait for cube to heat up, then hold thermomoter against each of 4 vertical faces of cube. You should find all faces are same temp
4= Hold infrared detector at set distance of 10cm away from one cubes vertical face and record amount of IR radiation it detects
5= Repeat measurement for each of cubes vertical faces. Making sure position of detector is same each time.
6= you should find you detect more infrared light from black surface than white one, and more from matte surface than shiny one.
7= Do experiment more than once to make sure results are repeatable
8= be careful don't move cube when full of water.
149
How to investigate how absorption depends on surface
1= stick ball bearings to back of 2 different surface with wax
2= see which one falls of first when surfaces placed at equal distances from bunsen burner
150
What is a perfect black body?
Object that absorbs all of the radiation that hits it. No radiation is reflected or admitted.
They are the best possible emmiters of radiation
151
Why do all objects emit EM radiation
Due to energy in thermal energy stores . Radiation is not just in infrared pat of spectrum it covers range of wavlengths and frequencies
152
What does intensity and distribution of wavlengthsemmited by an object depend on?
Objects temperature.
Intensity is the power per unit area.
153
What happens as temperature of an object increases?
The intensity of every emmited wavlength increases
154
What causes peak wavelength to decrease
When intensity increases more for shorter than longer wave lengths
155
What does intensity and wavlength of black body depend on?
Depends on temperature
156
What does overall temperature of Earth depend on?
Amount of radiation it reflects absorbs and emits.
157
During the day what happens to the local temperature?
It increases because lots of radiation like light is transferred to the Earth from sun and absorbed.
158
At night what happens to local temperaure?
It decrease, as less radiation is being absorbed than is being emmited
159
Overall what is the temperature of the earth like?
Fairly constant
160
What do changes to the athmosphere cause?
A change to the Earths overall temperature.
If athmosphere absorbs more radiation without emmiting the same amount the overall temp rises until absorption and emmisions are equal again (global warming)
161
What are sound waves caused by?
Vibrating objects. These vibrations are passed through the surrounding medium as a series of compressions and rarefractions.
162
What type of waves is sound waves?
longitudinal waves
163
Where does sound travel faster?
In solids than liquids and faster in liquids than gases.
164
How does a sound wave travel through a solid?
When sound wave hits solid object air particles hitting object causes particles in the solid to move back and forth and vibrate
The particles hit next particles in the line passing soundwave through the object as a series of vibrations
165
What does a paper diaprham in a speaker do?
Vibrates back and forth.
Creates surrounding air to vibrate creating compressions and rarefactions.
So sound wave is created
166
Why can sound not travel in space?
mostly a vaccum so there are no particles to move or vibrate
167
How can you hear sound when you ear drums vibrate?
Sound waves that reach your eardrum can cause it to vibrate
Vibrations are passed to tuny bones is ear called ossicles through semicircular canals and to the cochlea
Cochlea turns these vibrations into electrical signals which get sent to brain and allow you to sense the sound
Different materials convert different frequencies of sound waves into vibrations.
Humans hear sound from 20Hz-20khz
human hearing limited by size and shape of ear drum and structure of parts in ear that vibrate to trasnfer energy from the sound wave
168
What are sound waves reflected by?
hard flat surfaces, echoes are reflected sound waves
169
What happens to sound waves when they enter a different media?
They refract, and as they enter denser material they speed up.
As when waves travel in a medium wavelength changes but freuqency remains same so speed must change.
170
What is ultra sound?
Sound with frequencies higher than 20,000 Hz
Electrical devices can be made which produce electrical oscillations over range of frequencies. They can be converted into mechanical vibrations to make sound waves beyond human range of hearing.
171
What is partial reflection?
When a wave passes from one medium to another
Some of the waves are reflected off the boundary between the two media and some is transmitted and refracted
172
How does ultrasound get reflected back?
So you can point a pulse of ultrasound at an object and wherever there are boundaries between one substance and another som ultrasound gets reflected back.
Time taken for reflecetion to reach a detector can be used to measure how far away boundary is
173
How is ultrasound used for medical imaging?
Ultrasound waves can pass through the body but whenever they reach a boundary between two different media like fluid in womb and kin in foetus som wave is reflected back and detected.
The exact timing and distribution of these echoes are processed by a computer to produce video image of foetus
174
How ultrasound is used in indsutrial imaging for finding flaws in material
Ultrasound can be used to find flaw in objects like pipes or materials like wood or metal
Ultra sound waves entering material will be reflected by the farside of meterial
If there is a flaw like a crack inside material the wave will be reflected sooner
175
What does echo sounding use?
High frequency sound waves, used by boats and submarines to find out depth of the water they are in or locate objects in deep water
176
Distance equation
distance
## Footnote
speed x time
distance = speed/time
For a reflection question remeber the scale factor of 2
177
What happens when a wave arrives at a boundary?
Can be completely reflected or partially reflected
Wave may continue travelling in same direction but at different speed or it may be refracted or absorbed
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What does an earthquake produce?
Seismic waves, which travel out through the Earth. We detect these waves all over surface of planet using seismometers
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What do seismologists work out?
Time it takes for shock waves to reach seismometer.
And note which parts of the Earth don't recieve shock waves at all.
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What happen when seismic waves reach a boundary between different layers of material inside Earth
Some waves are absorbed and some refracted
Most of time if waves refracted they gradually change speed resulting in curved path.
But if properties change suddenly wave speed changes abruptly and the path has a kink
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Name the two different type of seismic wave
P waves
S waves
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By observing how seismic waves have absorbed and refracted what have we worked out?
Where properties of Earth changes dramatically.
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4 facts about P waves
longitudinal
Travel through solids and liquids as they pass through core
Travel faster than S Waves
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Give 4 facts about S Waves
Transverse
Can't travel through liquids or gases
Slower than P waves
Can't pass through liquid outer core only through solids
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