Waves Flashcards
1
Q
What do waves transfer from one place to another?
A
Energy
2
Q
What do we interpret the energy from waves as?
A
Meaningful information
—> why our brain is able to build up images and tunes from the light and sound that it receives
3
Q
How do waves travel from one place to another?
A
They vibrate or oscillate
4
Q
What is amplitude?
A
The height of a wave from the middle to the top (crest) or the bottom (trough)
5
Q
What is the wavefront?
A
An imaginary line that joins all the pointe where the wave is at the same part of the cycle
E.g. all the crests
6
Q
What is frequency?
A
The number of complete oscillations per second
7
Q
What is wavelength?
A
Distance of the entire oscillation (distance between two matching points)
E.g. one crest to the next crest
8
Q
What is the time period of a wave?
A
Time it takes for one complete oscillation
9
Q
What do waves not transfer?
A
Matter
10
Q
What is displacement?
A
How far from the equilibrium point the wave has oscillated
(How far it’s gone up or down)
11
Q
What is distance?
A
How far the wave has travelled from its starting point
Measures in metres (m)
12
Q
Equation for frequency
A
Frequency = 1/time period
f=1/T
13
Q
What is frequency measured in?
A
Hertz (Hz)
14
Q
Equation for time period
A
Time period = 1/frequency
T=1/f
15
Q
What is wave speed measured in?
A
metres per second (m/s)
16
Q
What is wavelength measured in?
A
Metres (m)
17
Q
What is a transverse wave?
A
Oscillations are perpendicular to the direction of energy transfer (direction in which the wave is moving)
18
Q
What kind of wave are most waves?
A
Transverse
19
Q
Examples of transverse waves
A
Electromagnetic - light, radio
Ripples/waves in water
Waves of strings - on a guitar
20
Q
What is a longitudinal wave?
A
Oscillations that are parallel to the direction of energy transfer
21
Q
Examples of longitudinal waves
A
Sound waves
Some types of shock waves - seismic p waves
22
Q
Electromagnetic waves are all …
A
Transverse waves
23
Q
What is the electromagnetic spectrum in order of?
A
Increasing frequency (decreasing wavelength)
24
Q
What is the order of the electromagnetic spectrum
A
Radio waves
Microwaves
Infrared
Visible light
Ultraviolet
X-rays
Gamma rays
25
In a vacuum what does the electromagnetic spectrum all travel at the same of?
The same speed of 3 x 10(8) m/s
26
What does the electromagnetic spectrum all travel at different speeds in?
Different mediums (can lead to refraction)
27
How is the wavelength and frequency related?
Inversely related
28
What does inversely related mean?
If one goes up the other one goes down
29
Radio waves have the …
Biggest wavelength
Smallest frequency
30
Gamma rays have the …
Smallest wavelength
Biggest frequency
31
What part of the spectrum can our eyes detect?
Visible light
32
What do the different wavelength in visible light give us?
All of the different colours that we can see
33
Order of colours (visible light)
Red
Orange
Yellow
Green
Blue
Indigo
Violet
34
Which 3 electromagnetic waves are all ionising?
Ultraviolet
X-rays
Gamma rays
—> can cause damage to our cells
35
Which electromagnetic waves are both used in communication?
Radio waves
Microwaves
36
Where do electromagnetic waves come from?
Everywhere
37
Which electromagnetic waves are emitted when there’s radioactive decay?
Gamma rays have been emitted
38
Which electromagnetic waves are emitted when electrons drop down energy levels (shells)?
Visible light
Ultraviolet
X-rays
39
Which electromagnetic waves are emitted when bonds holding molecules together vibrate?
Infrared
40
What can happen when waves come into contact with something?
Either be:
Reflected
Absorbed
Transmitted
—> or sometimes a combination of all three might happen
41
What are radio waves made up of?
Oscillating electric and magnetic fields
42
How can you generate radio waves?
By using electricity in the form of an alternating current
43
What is an alternating current made up of?
Oscillating charges
44
What does an oscilloscope do?
Allows us to see the frequency of the alternating current
—> determines the frequency of the wave
45
What does a receiver do?
Absorbs the energy and generates another alternating current
46
What do radio waves allow us to transfer?
Information
47
What are the three types of radio waves for communication?
Long waves
Short waves
Very short waves
48
How far can long waves be transmitted?
Huge distances, without having to interact with anything along the way
E.g. London —> Singapore
49
50
How do long waves work?
They diffract (bend) around the curved surface of the earth
51
What are long waves good for?
Long range communication
52
How far can short waves be transmitted?
Long distances and short distances
53
Example of short distances for short waves
Bluetooth in your phone
54
What are short waves not able to do?
Curve around the earth
55
How do short waves work?
They are reflected from the ionosphere and by bouncing back and forth repeatedly they can cover long distances
56
What is the ionosphere?
An electrically charged layer of the earth’s upper atmosphere
57
What are very short waves used for?
TV and FM radio
58
What do very short waves have to travel directly from and to?
Directly from the transmitter to the receiver (TV, FM radio)
59
Why is the signal not always great when you’re in the car?
Because the (very short) waves have to travel directly from the transmitter to the receiver and surrounding structures like hills and tunnels can get in the way of that direct transmission
60
Microwaves have …
Long wavelengths
Low frequency
61
Infrared have …
Long wavelengths
Low frequency
62
What are microwaves that aren’t absorbed by water molecules used for?
Communication using satellites
63
For satellites why do the microwaves have to not be able to be absorbed by water molecules?
Satellites are very far above the Earth and so the microwaves have to,pass through the earth’s atmosphere
—> wouldn’t be possible if they were absorbed by water molecules (atmosphere contains a lot of water)
64
How do microwaves used for communication through satellites work?
When the microbes make it through the atmosphere they are received by the satellite and then they’re transmitted back down to earth
- we can detect them using a satellite dish (to get things like satellite TV)
65
What are microwaves that are absorbed by water molecules used for?
Microwave ovens to help heat up our food
66
Why are microwaves that are absorbed by water molecules used in microwave ovens?
Most of the food we eat contain lots of water molecules
—> when microwaves are fired at our food, the energy from those waves gets absorbed by all the water molecules
67
How do microwave ovens work?
1) fire the waves at our food and the energy from those waves gets absorbed by all the water molecules
2) water molecules start to vibrate more with all the new energy
3) they transfer some of the energy to neighbouring molecules so it spreads throughout food via conduction and convection
68
What do foods that contain more water tend to do?
Heat up more quickly in the microwave
69
Where is infrared radiation emitted from?
All objects that have thermal energy
70
What does the amount of infrared radiation that gets emitted depend on?
The object’s temperature
—> the hotter the object the more infrared radiation it will emit
71
What are 3 uses of infrared radiation?
Infrared cameras
Cooking
Electric heaters
72
What are 2 uses of microwaves?
Communication using satellites
Microwave ovens
73
What do infrared cameras do?
Help us to see in the dark (help us spot living organisms)
74
What can we see in infrared cameras?
Which areas are hot and which areas are cold
75
How do we know which areas are hot and which areas are cold in an infrared camera?
By measuring how much infrared radiation they emit
76
How do animals appear in an infrared camera?
Quite bright because they emit lots of infrared radiation as they are warm
77
How do the animals’ surroundings appear in an infrared camera?
Darker because they don’t emit as much radiation
78
How is infrared radiation used in cooking?
By heating metal to very high temperatures (ovens + grills) we can make the metal emit lots of infrared radiaiton
—> which can then heat our food by transferring the heat energy
79
What does infrared radiation not do?
Penetrate the surface of food
—> why bread toast in a toaster rather than just warming up (like in a microwave)
80
Why does bread toast in a toaster rather than just warming up like in a microwave?
Infrared radiation doesn’t penetrate the surface of the food
81
What do electric heaters do and how do they work?
Use electrical energy to the heat up the metal of the heater
—> because of the heat it emits infrared radiation to the surroundings (able to heat up our rooms)
82
When are microwaves and infrared waves only harmful to us?
In high quantities
- background radiation doesn’t do us any harm
83
What would happen if you put living cells in a microwave?
They’d boil and be destroyed
84
What would happen if you put you hand in a toaster/grill?
You’d get burns
—> all the nearby skin cells would get destroyed
85
What is visible light?
The light we use to see
86
Visible light appears as different colours depending on what?
The wavelength
87
Which colour has the longest wavelength?
Red
88
Which colour has the shortest wavelength?
Violet
89
Order of colours and their wavelength (biggest to smallest)
Red
Orange
Yellow
Green
Blue
Indigo
Violet
90
What can visible light be used for?
Communication
Photography
91
How is visible light used for communication?
Using optical fibres
92
What are optical fibres?
Thin glass/plastic fibres that are able to transmit pulses of light over long distances
93
How do optical fibres work?
1) they transmit pulses of light over long distances
2) the light is reflected every time it hits the surface
3) ends up bouncing back and forth throughout the entire journey until it emerges at the other end of the fibre where it can be interpreted
94
By encoding information into light pulses we can use optical fibres to …?
Transit data really quickly over long distances
95
Which materials do you have to use for optical fibres?
Materials that will totally reflect the light rather than absorbing any
—> also ensure the reflection is specular rather than diffuse - so the light isn’t scattered at all
—> materials have to be smooth and flat
96
What is alternative to using optical fibres?
Using copper wires and electricity
97
What are advantages of using optical fibres?
Can transmit much more information
Signals are less likely to be distorted during transmission
98
How is visible light used in photography?
Uses visible light to create images
99
How does photography work with visible light?
1) light is reflected off objects and is refracted into (bends into) the camera lens which focuses light on to a sensor
2) the sensor detects the brightness and colour of the light to form a clear picture
100
What are 3 uses of ultraviolet waves?
Fluorescence (fluorescent lights)
Security
Sterilise water
101
Ultraviolet waves have a … than visible light
Shorter wavelength
Bigger frequency
102
Where is ultraviolet emitted from?
The sun
—> gives us a sun tan/burn
103
By generating ultraviolet radiation ourselves what can we use it for?
Sun beds
104
How does fluorescence work?
1) ultraviolet light is absorbed
2) then the energy is re-emitted as visible light
105
Why does fluorescent paint look very bright?
It is emitting light
—> most materials just reflect
106
How do fluorescent lights work?
1) generate UV radiation
2) which is then absorbed by a layer of phosphorus (which coats the inside of a glass bulb)
3) because the phosphorus has so much energy it re-emits it as visible light
Ultraviolet —> visible light
107
Why is phosphorus coated inside a glass bulb?
It glows when UV light hits it (called fluorescence)
Phosphorus absorbs the UV light and re-emits it as visible light
108
What are the benefits of using fluorescent bulbs?
Really energy efficient
—> can save on electricity bills and carbon dioxide emissions
109
How is ultraviolet light used in security?
Using special security pens
110
What are special security pens?
Write things that are completely invisible until we shine ultraviolet on them
111
How is UV light used in passports and bank notes?
They have special ink that only shows under UV light (so usually invisible)
—> making it hard to copy and easier to spot fakes
112
Where are UV light in security?
Passports
Banknotes
113
How is ultraviolet light used to sterilise water?
The UV destroys microorganisms
114
X-rays have the …
Shortest wavelength
Highest frequency
115
Gamma rays have the …
Shortest wavelength
Highest frequency
116
What do x-rays help us do?
View the internal structure of objects
117
How do x-rays work?
1) firing x-rays through a body and recording the ones that get through using a detector plate
118
What will the x-rays be absorbed by?
Dense materials (bones)
119
What will the x-rays pass straight through?
Parts that are mostly air (lungs, intestines)
120
Where do the x-rays only pass partially through?
Fleshy parts (heart)
121
How do x-ray images start off?
Completely white
122
The x-ray images will only go black if …?
That area of the detection plate receives radiation
123
Which areas appear white on an x-ray image?
Bones
124
Which areas appear black in an x-ray image?
Things surrounding the bone (background)
125
What are x-rays used to detect?
Broken bones
Other diseases
126
How much radiation are people exposed to during an x-ray?
A small amount that can be harmful
127
Why is it worth taking the risk when having an x-ray?
The dose is very low
128
Benefits of x-rays
Quick and cheap test
129
Who is the danger much higher for in an x-ray?
The staff involved
130
What do staff do during x-rays?
Wear lead aprons to stop the x-rays
Leave the room when the x-rays are being fired
131
What are gamma rays used for?
Sterilise medical equipment and food
132
Why are gamma rays used for sterilisation?
They can kill microorganisms without causing any other damage
133
What is another option to kill any harmful microbes on medical equipment?
Use boiling water
134
Why can’t you always use boiling water to sterilise medical equipment?
Some materials like plastic can get damaged
—> can melt slightly
135
Why are gamma rays mainly used for medical sterilisation rather than boiling water?
They do no damage
—> no risk
136
Why are gamma rays used to sterilise food?
Kill the harmful microbes without altering the food in any way
137
Why are gamma rays used to sterilise food?
Keeps food fresh for longer
—> no microorganisms left to start breaking it down
—> still perfectly safe to eat
138
What are x-rays and gamma rays both types of?
Ionising radiation
139
Since x-rays and gamma rays are both ionising what can they do?
Damage our cells
—> rare cases - lead to cancer
140
What are all objects constantly doing?
Absorbing and emitting electromagnetic radiation with its surroundings
141
What will happen if an object is absorbing something?
Will get warmer
142
What will happen if an object is emitting something?
Will cools down
143
Radiation is …
Pure energy
144
The balance between absorbing and emitting radiation will the affect the object’s …?
Temperature
145
Hot objects (tea)
Hotter than its surroundings
—> so more radiation is emitted than absorbed
Will lose energy and cool down
146
Cold objects (ice)
Cooler than its surroundings
—> so more energy is absorbed than emitted
Will gain energy and warm up
147
What happens to objects that absorb and emit the same amount of energy?
They will stay the same temperature
148
Why do objects that absorb and emit the same amount of energy stay the same temperature?
They are gaining and losing the same amount of heat
149
What does intensity mean?
How much energy the radiation transfers to a given area in a certain amount of time
150
As the temperature of the object increases the …?
Intensity of every emitted wavelength increases as well
151
Why do shorter wavelengths shift to the left?
The intensity of the shorter wavelength increases
152
Bunsen burner: the hotter the flame the …
Shorter the wavelengths of light emitted
153
What type of radiation is emitted from objects at room temperature?
Infrared - why we can’t see the emitted radiation
154
The shorter the wavelengths …?
The higher the energy (hotter the object)
155
Why is a blue Bunsen flame hotter than a red one?
Blue light has a shorter wavelength so has more energy (heat)
156
What does Earth absorb and emit?
Absorbs: electromagnetic radiation from the sun
Emits: its own infrared radiation (it’s a big warm object)
157
What can the atmosphere do with radiation?
Reflect
Absorb
Emit
158
During the day:
More energy is ABSORBED by the earth and atmosphere than is being emitted
—> increases the local temperature
159
During the night:
Less energy is absorbed
More energy is EMITTED
—> decreases the local temperature
160
Why does the overall temperature of Earth stay pretty constant?
Some part of the earth is always in the sun
161
Waves are either:
Absorbed
Transmitted
Relfected
162
What does absorbed mean?
Energy from the wave is transferred to that material’s energy stores
163
What does transmitted mean?
The wave enters the material but carries on travelling and passes out the other side
—> leads to refraction
164
What does reflected mean?
Wave enters the material
165
What happens to the wave depends on …?
The wavelength of the wave involved
The properties of the two materials
166
What is the law of reflection
Angle of incidence = angle of reflection
(ALWAYS THE SAME SIZE ANGLE)
167
168
What is the point of incidence?
The point where the rays touch the normal
169
What is the name of the ray when it bounces of the normal?
Reflected ray
170
What is a specular reflection?
When light reflects off a smooth surface and bounces off at the same angle it came in
—> angle that the light hits the surface is the same as the angle at which it reflects (e.g. comes in at 45 degrees, bounces off at 45 degrees)
Both measured from a line that’s perpendicular (90 degrees) to the surface
—> straight line in the middle
Creates a clear image
171
What is the boundary like in a mirror?
Flat
Normals are all in the same direction
172
What is a diffuse/scattered reflection?
Light hits a rough surface and bounces off at a different angle/direction
Doesn’t form a clear image
173
What is the boundary like in paper?
Bumpy
Normals will all be different
174
What is refraction?
When waves change direction as they pass from 1 medium to another
E.g. air into glass
175
Waves travel at different speeds in different …?
Materials (mediums)
—> different mediums have different densities
176
The higher the density of the material the …?
Slower the light wave will travel through it
177
Air has a …?
Low density
178
Glass has a …?
High density
179
What happens when a wave travels through air (low density) and then through glass (high density)?
It will slow down
180
What happens when a wave travels through air (low density) and then through glass (high density)? AT AN ANGLE
It will bend towards the medium
181
What is the incoming ray also known as?
The incident ray
182
What is the angle between the incident ray and the normal called?
Angle of incidence
183
What is the ray called when it travels through the high density medium (refraction)?
Refracted ray
184
What is the angle between the normal and the refracted ray called?
Angle of refraction
185
What is the ray called when it leaves the high density medium into the air again (refraction)?
Emergent ray
186
Equation for wave speed
Wave speed = frequency x wavelength
v = f x /^\
187
What happens if the speed of the wave increases?
The wavelength also increases
188
What does white light contain?
All the wavelengths of visible light
189
What happens if white light travels through a triangular prism?
The different colours will bend to different degrees
—> will spread out like a rainbow
190
Different wavelengths of light are …?
Refracted by different amounts
191
What is the refractive index of a material?
A measure of the speed of light as it passes through the material compared to the speed of light as it passes through a vacuum
192
What do materials through which light travels more slowly have?
A higher refractive index
193
Diamonds have a …?
Higher refractive index
—> 2.4
194
What do materials through which light travels more quickly have?
A lower refractive index
195
Water has a …?
Lower refractive index
—> 1.3
196
Which medium has the lowest refractive index?
A vacuum
197
What does light travel fastest in?
A vacuum
198
What is vacuums refractive index?
1
199
Equation for refractive index
Speed of light in a vacuum
—————————————
Speed of light in the material
n=c/v
200
What does ‘n’ stand for?
Refractive index
201
What does ‘c’ stand for?
Speed of light in a vacuum
202
What does ‘v’ stand for?
Speed of light in that material
203
What is Snell’s law?
Equation linking the refractive index (n), the angle of incidence (i) and the angle of refraction (r)
204
Equation for Snell’s law
sin (i)
n = ———
sin (r)
