Section 2 - Waves and the Electromagnetic Spectrum Flashcards
1
Q
What happens when a wave travels through a medium?
A
The particles of the medium vibrate and transfer energy and information between each other
2
Q
What do waves transfer?
A
Energy and information
3
Q
What doesn’t change when a wave travels through a medium?
A
The particles location
4
Q
What is the amplitude of a wave?
A
The displacement from the rest position to a crest or trough
5
Q
What is the wavelength of a wave?
A
The length of a full cycle of the wave
6
Q
What is the frequency of a wave?
A
The number of complete cycles of the wave passing a certain point per second
7
Q
What is the period of a wave?
A
The number of seconds per cycle
8
Q
What is the relationship between frequency and the period of a wave?
A
They are inverse
9
Q
What is the period equation?
A
Period = 1 / Frequency
10
Q
What direction vibrations do transverse waves have?
A
Perpdenciular to the direction the wave travels
11
Q
Give examples of transverse waves
A
EM Waves
S Waves
Ripples and waves in water
12
Q
What direction vibrations do longitudinal waves have?
A
Parallel to the direction the wave travels
13
Q
Give examples of logitudinal waves
A
Sound Waves
P Waves
14
Q
What are the compressions in longitudinal waves
A
The squashed up areas of the wave (high pressure with lots of particles)
15
Q
What are the rarefactions in longitudinal waves?
A
The stretched out areas of the wave (lower pressure with fewer particles)
16
Q
What is the equations for wave speed?
A
V = F x λ m/s = Hz x m
V = x / t m/s = m / s
17
Q
A wave has a speed of 0.15 m/s and a wavelength of 7.5 cm
Calculate it’s frequency
A
cm -> m
7.5/100= 0.075
v / λ = f
0.15 / 0.075 = f
2 Hz
18
Q
What can you use to measure the speed of sound?
A
An oscilloscope
19
Q
To measure the speed of sound what apparatus do you need?
A
A signal generator
Speaker that can generate sounds with a specific frequency
Two microphones
An oscilloscope
20
Q
How do you setup the oscilloscope when measuring the speed of sound?
A
So the detected waves at each microphone are shown as separate waves
21
Q
What do you do with the microphones when measuring the speed of sound?
A
Slowly move one away until the two wavess are aligned but have moved one wavelength apart
22
Q
When measuring the speed of sound, what is one wave length equal to?
A
The distance between the microphones
23
Q
When measuring the speed of sound, state all the measurements you need at how you get them?
A
Frequency - the frequency you set the frequency to on the speaker
Wavelength - the distance between the microphones, once they match up on the oscilloscope with one being one wavelength ahead
24
Q
What do you use to measure the speed of water ripples?
A
A strobe light
Signal genertor
Ripple tank with a dipper
25
What do you do with the strobe light when measuring the speed of water ripples?
Alter the strobe lights' frequency until it matches the ripples' frequency
26
How do you tell the frequency of the strobe light and the ripples are the same?
The wave pattern on the screen will appear to freeze and stop moving
27
Why does what happens when the frequency of the strobe light and the ripples are the same happen?
The light lights up the waves at the same point in there cycle each time
28
When measuring the speed of water ripple what measurements must you have and how do you get them?
Frequency - The frequency you set tthe dipper to
| Wavelength - Measure the wavelength of 10 lines apart and then find the average wavelength
29
What method do you use to find the speed of waves in solids?
Peak Frequency
30
When measuring the speed of waves in solids, what measurements must you take before hand?
The length of a metal rod
31
Tap the ___ with the ______
Tap the rod with the hammer
32
What does tapping the rod with a hammer give you?
The peak frequency
33
How many times should you repeat the peak frequency method?
Three times
34
How do you calculate the speed of a wave in solids?
Using v = fλ
| λ is equal to twice the length of the rod
35
What is λ equal to when finding the speed of waves in solids?
Twice the length of the rod
36
λ is equal to ____ the length of the rod
λ is equal to twice the length of the rod
37
Describe an experiment to measure the wavelength of a water wave
Add water to a ripple tank with a signal generator
Set strobe light to frequency of dipper, you can tell when they're in sync when the waves don't appear to move
Measure the wavelength of 10 waves and then calculate and average
Times that by the frequency of the dipper to calculate wave speed
38
What can happen to waves when they meet boundaries?
Reflected
Absorbed
Transmitted
39
How do you remember what happens to waves when they meet boundaries?
R.A.T (Toby)
40
What happens when a wave us absorbed?
The wave transfers energy to the materials energy stores
41
What happens when a wave is transmitted?
The wave carries on travelling through the new material
42
What does wave transmission lead to?
Refraction
43
What is refraction used in?
Communications
Glasses
Cameras
44
What happens when a wave is reflected?
The wave is neither absorbed or transmitted instead it is sent back away from the second material
45
What is an example of a wave being reflected?
An echo
46
What is refraction?
Waves changing directions at a boundary
47
Waves travel at _______ speeds in materials with ______________
Waves travel at different speeds in materials with different densities
48
When does refraction not occur?
When a wave travels along the normal or when the densities of the two mediums are the same
49
The _______ the change in speed, the more a wave bends
The greater the change in speed, the more a wave bends
50
Compare the speed of EM waves in a vaccum to a denser material
EM waves travel slower in denser materials
51
What affects how much an EM wave refracts?
Wavelength
52
How does wavelength affect refraction?
The shorter the wavelegnth, the more the wave bends
53
What stays the same as the wave passes the boundary?
It's frequency
54
In terms of refraction, what is the relationship between wavelength and velocity?
As wavelength decreases, velocity decreases
| As wavelength increases, velocity increases
55
What is the name of the ray that meets the normal at the boundary?
The incident ray
56
What is the angle of incidence?
The angle between the incident ray and the normal
57
What will happen to a light wave if it passes from a less dense to a more dense medium?
It will move towards the normal
58
What will happen to a light wave if it passes from a more dense to a less dense medium?
It will move away from the normal
59
Give an example of a low density medium
Air
60
Give an example of a high density medium
Glass
61
If a wave speeds up when it passes through a medium where does it bend to?
Away from the normal
62
If a wave slows down when it passes through a medium where does it bend to?
Towards the medium
63
How does Izak remember what happens with the speed of a wave and refraction?
Like a graviational pull, if you go fast enough you can escape if you don't you get pulled in
64
A light ray enters air from water at 50* to the nrmal
| How does it bend relative to the normal?
Away from the normal as gains speed
65
What are sound waves caused by?
Vibrating objects
66
What are the sound vibrations passed thorugh as?
A series of compressions and rarefactions
67
What determines which frequencies and object can transmit?
Size
Shape
Structure
68
Compare the speeds of speed in the different states?
Fastest in solid, medium in liquid and slowest in gas
69
What doesn't change when a wave pases from one medium to another?
Frequency
70
What are reflected sound waves called?
Echoes
71
What type of objects cause sound waves to reflect?
Hard and flat
72
When do you hear sound?
When the ear drum vibrates
73
List the path sound takes in the ear
Outside Ear -> Eardrum -> Ossicles -> Semicircular Canals -> Cochlea -> Brain
74
What is the role of the eardrum in the ear?
To vibrate the sound into the ear
75
What are the name of the tiny bones in your ear?
The ossicles
76
What turns the sound into the electrical signals which is then sent to the brain?
The cochlea
77
What is the electrical signals for sound sent along?
The auditory nerve
78
What determines the pitch of a sound?
It's frequency
79
What determines the volume of a sound?
It's amplitude
80
What limits human hearing?
The size and shape of the eardrum
| The structure of all the parts within the ear that vibrate to transmit the sound wave
81
Describe how you hear a sound wave
The sound enters the ear and vibrates the ear drum, which then vibrates the ossicles then the semicircular canals and then the cochlea
The cochlea then converts the sound to electrical signals which is sent along the auditory nerve to the brain
82
What happens to ultrasound waves when they hit boundaries?
They get partially reflected
83
What is partial reflection?
When a wave crosses a medium and some of the wave is reflected off the boundary whilst some is transmitted
84
What hertz is ultrasound?
Any frequency higher than 20,000 Hz
85
How is ultrasound useful?
Medical imaging
Industrial imaging
Sonar
86
How is ultrasound used for medical imaging?
Ultrasound is passed through the body but bounces of certain materials
A computer processes this infomation and produces a video image
87
How is ultrasound used for industrial imaging?
Ultrasound is used to find flaws in objects as they will enter the material and will usually be reflected by the far side of the material
However, if there is a flaw it will be reflected sooner
88
What is sonar used for?
To find out the deepness of the water and to locate objects in deep water
89
A pulse of ultrasound takes 4.5 seconds to travel from a submarine to the sea bed and back again
If the speed in sea water is 1520 m/s, how far away is the submarine from the seabed?
```
S = 2D / T
2D = S x T
2D = 6840 m
D = 3420 m
```
90
What is infrasound?
Sound with frequencies lower than 20 Hz
91
What are examples of natural uses of infrasound?
```
Animal communication (eg. Elephants and Whales)
Natural Disasters (eg. Volcanoes, Earthquakes and Avalanches)
```
92
How do scientists predict natural events?
Because these events produce infrasound
| Scientists can monitor infrasound to predict it
93
What happens when seismic waves reach a boundary between different layers of material?
They are absorbed or refracted
94
What type of seismic wave can travel through the Earth's core?
P-waves
95
What type of seismic wave can't travel through the Earth's core?
S-waves
96
What have scientists been able to work by observing seismic waves?
The internal structure of the Earth
| The size and material of the Earths' inner layers
97
What type of waves are P-waves?
Longitudinal
98
What types of state can P-waves travel through
Solids and liquids
99
Compare the speed of P-waves to S-waves
P-waves are much faster
100
What type of waves are S-waves
Transverse waves
101
What types of state can S-waves travel through?
Solid
102
Which seismic wave is transverse?
S-waves
103
Which seismic wave is longitudinal?
P-waves
104
Which seismic wave is faster?
P-waves
105
How do you remember which is the fastest seismic wave?
Primary means earliest in time meaning it is the first to get there which means it's the fastest
106
How do you remember which seismic wave is transverse or longitudinal?
S is next to T in the alphabet and S-waves are Transverse
107
How do you remember which seismic wave travels through which state of material?
S-waves travel through solids, S for solid
| Primary do everything
108
S-waves produced at the Earth's North Pole would not be detected at the South Pole
Suggest one conclusion you can make about the Earth's core from the observation
Explain your answer
S-waves can only travel through solids
| S-waves can't travel through the core, meaning atleast a bit of the core is liquid
109
What is the law of reflection?
Angle of incidence = Angle of reflection
110
What is the angle of incidence?
The angle between the incoming wave and the normal
111
What is the incident ray?
The incoming ray
112
What is the angle of reflection?
The angle between the reflected wave and the normal
113
What is the reflected ray?
The ray that is reflected off the boundary
114
What is the normal?
An imaginary line that's perpendicular to the surface at the point of incidence
115
What does TIR depend on?
The critical angle of the material
116
What is the critical angle of a material?
The angle at which the angle of refraction is 90* (perpendicular to the normal)
117
When does TIR happen?
When the angle a wave hits a less dense medium is greater than the critcal angle
118
What is TIR?
Total reflection of wave from a more dense medium to a less dense medium with no wave coming out instead it all internally reflects
119
Reflection can be _______ or _____
Reflection can be specular or diffuse
120
When does specular reflection occur?
When waves are reflected in a single drection by a smooth surface
121
When does diffuse reflection occur?
When waves are reflected by a rough surface
122
Why does diffuse reflection occur?
Because the normal is different for each incident ray meaning the reflection angle is different (angle of incidence = angle of reflection)
123
Name the type of reflection that occurs when waves are reflected by a smooth mirror
Specular
124
A light ray is incident on a mirror at an angle of 30*
| What will it's total angle be?
```
Reflection angle = 30*
∴
∠Reflection + ∠Incidence = Total Angle
30 + 30 = 60*
60*
```
125
When investigating refraction, why should a thin beam of light be used?
So you can easily trace the ray to measure the angle between the ray and the angle
126
What does the colour and transparency of light depend on?
It's wavelength
127
What are opaque objects?
Objects which do not transmit light
128
What do white objects do?
Reflect all wavelengths of light equally
129
What do black objects do?
Absorb all wavelengths of light
130
What type of objects transmit light?
Transparent/translucent objects
131
What do colour filters do?
Only let through particular wavelengths
132
If a red object was placed in front of a blue filter what colour would the object appear?
Black
133
Explain why a cucumber looks green?
Because it reflects green light but absorbs all other wavelengths of light
134
Give the two types of lens's
Converging (Convex)
| Diverging (Concave)
135
Describe a converging lens?
Bulges outwards in the middle
136
What does a converging lens do to light?
Converges it at the principal focus
137
Describe a diverging lens?
Caves inwards
138
What does a diverging len do to light?
Spreads it out
139
What is the principal focus of a converging lens?
The area where the rays parallel to the axis meet
140
What is the principal focus of the diverging lens?
The area where the rays parallel to the axis appear
141
How do you find the principal focus of a diverging lens?
Trace them back until they all appear to meet up at a point behind the lens
142
What is the focal length?
The distance from the centre of the lens to the principal focus
143
What is the unit for principal focus?
F
144
When is an image formed?
When all light rays from a certain point on an object appear to come together
145
Give the two types of images?
Real
| Virtual
146
When is a real image formed?
When lights rays actually come together to form the image
147
What type of image can be put onto a screen?
A real image
148
What type of image is found on the eye's retina?
Real
149
When is a virtual image formed?
When light rays from the object appear to be coming from a completely different place to where they're actually coming from
150
What type of image can't be put onto a screen?
Virtual
151
Give an example of an object which creates virtual images?
A magnifying glass
152
What increases the power of a lens?
Its curvature
153
Describe the relationship between power of lens and focal length
The more powerful the lens, the more strongly it converges rays of light, so the shorter the focal length
154
What lens has a positive power?
Converging
155
What lens has a negative power?
Diverging
156
How can you increase the power of a lens?
Change the material
| Increase it's curvature
157
What is the principal focus of a converging lens?
The point where rays hitting the lens parallel to the axis meet
158
What is the principal focus of a diverging lens?
The point where light rays hitting the lens parallel to the axis appear to come from
159
Describe the image produced from a diverging lens
Virtual
Right way up
Smaller
Same side of the lens
160
Briefly describe how to draw a ray diagram of a diverging lens?
Draw two rays, one from the object through the lens and the other parallel to the axis of the lens through the lens
Refract the line that went through the lens, that is parallel to the lens
Draw dotted line from 1F to refraced ray
The point where all three lines intersect is where the image is formed
161
What affects the image produced from a converging lens
Its distance from the object
162
Briefly describe how to draw a ray diagram of a converging lens?
Draw two rays, one from the object through the lens and the other parallel to the axis of the lens through the lens
Refract the line through 1F
The image will form when the refracted ray meets the ray that went straight through the lens
163
How will the object appear when 2F away from a converging lens?
```
Same size
2F away
inverted
Real
Other side of the lens
```
164
How will the object appear when 1F-2F away from a converging lens?
Real
Inverted
Bigger
Beyond 2F
165
How will the object appear when <1F away from a converging lens?
Virtual
Right way up
Bigger
Same side of the lens
166
On a ray diagram, what determines whether the image is upright?
If its above the axis
167
On a ray diagram, what determines whether the image is inverted?
If its below the axis
168
On a ray diagram, what determines whether the image is real?
If the image is past the lens
169
On a ray diagram, what determines whether the image is virtual?
If the image is before the lens
170
What kind of image does a diverging lens produce?
Virtual
171
Compare the speeds of EM waves?
The same in a vacuum
| But different in different materials
172
What do we group EM waves off?
Wavelength/frequency
173
How many EM waves are there?
7
174
Name all the EM waves
```
Radiowaves
Microwaves
Infrared
Visible light
Ultraviolet
X-rays
Gamma rays
```
175
What causes the generation of EM waves?
Changes in atoms and their nuclei
176
What creates gamma rays?
Changes in an atoms nucleus
177
What creates visible light?
Changes in an electrons energy level
178
What does the higher frequency mean of a wave?
The more energy it transfers
179
What EM wave transfers the most energy?
Gamma rays
180
Describe the interaction between the human body and radio waves
No harm as the waves are transmitted fully
181
Describe the interaction between the human body and microwaves
Some wavelengths can be absorbed, causing the heating of cells
182
What can some wavelenghts of microwaves do to the body?
Heat the cells
183
Describe the interaction between the human body and infrared
Mainly reflected but can be absorbed causing heating, which may cause burns if the skin gets too hot
184
Describe the interaction between the human body and visible light
Mainly reflected but can be absorbed causing heating
185
Describe the interaction between the human body and ultraviolet
Absorbed by the skin which can cause damages to cells and could lead to skin cancer
186
Why is ultraviolet much more dangerous than IR?
Because it has a higher frequency meaning its more ionising
187
What can UV cause to the human body?
Skin cancer
| Eye conditions and blindness
188
Describe the interaction between the human body and x-rays
Absorbed which can cause mutations and damage cells
189
Describe the interaction between the human body and gamma rays
Absorbed which can cause mutations and damage cells
190
Explain why gamma rays are more dangerous to humans than visible light?
Gamma rays are ionising so they can cause tissue damage and cancer but visible light isn't ionising
They carry more energy than visible light, so their potential for damage is higher
191
What does every object absorb and emit?
EM radiation
192
What does the distribution and intensity of wavelengths depend on?
The objects temperature
193
What is intensity?
The power per unit area
194
What happens to the object as the temperature increases?
The intensity of every emitted wavelength increases
195
Compare the intensity of different wavelengths emitted when the object is increased?
The shorter the wavelength the faster the intensity increases
196
Describe an object with constant temperature in terms of emission and absorption
Absorption = Emission
197
Describe an object that is heating up in terms of emission and absorption
Absorbing > Emitting
198
Describe an object that is cooling down in terms of emission and absorption
Emitting > Absorbing
199
Where does the Earth get most of its radiation from?
The Sun
200
What happens to the radiation the Sun gives to the Earth?
Some reflected
| Most absorbed
201
What does the reflected radiation do to the Earth?
Reflect out to the Earth's atmosphere,clouds and surface which will cause an increase in temperature
202
What happens to the absorbed radiation in the clouds/atmosphere?
Is emitted at night causing a decrease in the temperature
203
What type of surfaces are the best emitters?
Black
204
Briefly describe how to investigate how well different surfaces emit radiation?
Fill identical test tubes with hot water whilst surrounding them with different types/colours of materials (eg. Black, White, Glossy and Matte paper)
Measure the temperature, the one with the greatest temperature drop is the best emitter, the one with the lowest temperature drop is the best insulator
205
What will emit better: Shiny or matte surfaces?
Matte
206
What will emit better: White or black surfaces?
Black
207
Explain what is happening in terms of radiation and temperature when a bowl of ice cream is left on a counter in a warm room?
The bowl of icecream is absorbing more infrared radiation than it is radiating
This causes an increase in the temperature of the bowl of ice cream
208
What are EM waves made of?
Oscillating electric and magnetic fields
209
What make up oscillating charges?
Alternating currents (AC0
210
What happens when charges oscillate?
They produce oscillating electric and magnetic fields
211
The frequency of the waves produced will equal ________________
The frequency of the waves produced will equal the frequency of the alternating current
212
What is a transmitter, when making radio waves?
The object in which charges oscillate to create the radio waves
213
Describe how radio waves are converted into a current
A reciever absorbs radio waves
The energy carried by the waves transfers to the electrons in the matierla causes the electrons to oscillate, generating an alternating current
214
What are radio waves mainly used for?
Communication and broadcasting
215
What are the wavelengths of long-wave radio waves?
1-10km
216
What is the name for when a wave bends
Diffraction
217
Why can long-wave radio waves go halfway around the world?
Because they can diffract around the curved surface of the Earth
218
What are the wavelengths of short-wave radio waves?
10-100m
219
How do short-wave radio waves go across the world?
By being reflected by the Earth's atmosphere
220
What type of wave does bluetooth use?
Short-wave radio waves
221
Describe the wavelength for TV and FM radio transmissions
Very short
222
What must waves, that are used for communication to and from satellites, be able to do?
Easily pass through the Earth's watery atmosphere
223
Explain why signals between satellites are usually transmitted as microwaves
They can easily pass through the Earth's watery atmosphere without being absorbed
224
How do microwaves work?
The microwaves transmit a few centimeters into the food before being absorbed and transferring the energy they are carrying to the water molecules, heating up the food
225
Describe the difference between microwaves in ovens and in satellites?
The ones with satellites must be able to pass through the atmosphere,. whereas, the microwaves in microwaves need to be absorbed by water molecules
226
Give uses of microwaves
Communication
| Microwave ovens
227
What gives out infrared radiation?
All warm objects
228
Give uses of infrared radiation?
```
Burgular alarms
Thermal imaging
Short range communication
Cooking
Optical fibres
```
229
What do infrared cameras do?
Detects IR and converts it into an electrical signal which is displayed on a screen
230
How do infrared sensors work?
By detecting a change in infrared radiation and then sounding an alarm or a security light
231
How is infrared used for cooking?
Infrared causes objects to get hotter meaning adding IR to food will cause it to heat up
232
What are the disadvantages of using infrared to transfer information?
Must be a short distance
| Must be in line of sight
233
What are optical fibres?
Thin glass or plastic fibres that carry data over long distances
234
What do optical fibres rely on?
Total Internal Reflection
235
Why do optical fibres use a single wavelength?
To prevent dispersion which can otherwise cause some information to be lost
236
Give three uses of infrared radiation
```
Any three from:
Burgular alarms
Thermal imaging
Short range communication
Cooking
Optical fibres
```
237
What does photography rely on?
Visible light
238
What are uses of visible light?
Photography
239
How does photographic film work?
By reacting to light to form an image
240
How do digital cameras work?
By using image sensors to detect visible light and generate an electrical signal which is then converted into an image
241
What is ultraviolet used in?
Fluorescent lamps
Bank notes/passports
Security pens
Sterilising water
242
What is fluorescence?
A property of chemicals where UV radiation is absorbed and then visible light is emitted
243
How is UV used to sterilise water?
It's blasted onto water killing any bacteria in it
244
What are x-rays used for?
To view the internal structure of objects and materials
245
How do radiographers take x-ray images?
The patient is placed on a detector plate whilst x-rays are directed onto the body, the x-rays transmit through the flesh and are absorbed by denser material (eg. Bones and Metal) meaning the image will pick up areas of high x-ray amount meaning low density material (eg Flesh) and areas of low x-ray amount meaning high density material (Eg. Bones and Metal)
246
What are gamma rays used for?
Sterilisation
Medical imaging
Cancer treatments
247
How are gamma rays used in sterilisation?
They kill microbes
248
What are the benefits of using gamma rays to steralise food?
No need to freeze it, cook it or preserve it some other way
249
Give examples of gamma being used in medical imaging?
PET scans and tracers
250
How are gamma rays used in cancer treatments?
Targeted at cancer cells to kill them
251
What are the cons of using gamma radiation for cancer treatment?
If not aimed correctly will cause damage to healthy cells
252
State two uses of ultraviolet radiation?
```
Any two from:
Fluorescent lamps
Security pens
Detecting forged bank notes
Sterilising water
```
253
Suggest one advantage of sterilising food with gamma rays
You don't have to freeze it/cook it/preserve it to keep it fresher for longer
254
What is the amplitude of a wave?
The displacement from the rest position to a crest or trough
255
What is the wavelength of a wave?
The length of a full cycle of the wave
256
What is the frequency of a wave?
The number of complete cycles per second
257
What is the period of a wave?
The number of seconds it takes for one full cycle
258
Describe the difference between transverse and longitudinal waves?
In longitudinal waves, the vibrations are parallel to the direction of wave travel.
In transverse waves, the vibrations are at right angles to the direction of wave travel.
259
What affects an objects ability to transmit given frequencies of sound?
It's size, shape and structure
260
What is the frequency of ultrasound?
> 20,000 Hz
261
What is the frequency of infrasound?
> 20 Hz
262
What conditions are needed for total internal reflection to occur?
The light must be travelling from a more dense medium into a less dense medium (eg. glass to air)
The angle of incidence must be greater than the critical angle.
263
Explain what happens to white light that hits a white object?
All of the light is reflected by the object
264
True or False? Diverging lenses always produce real images?
False
265
True or false? All EM waves are transverse?
True
266
Give one danger of UV radiation?
Any one from:
Skin cancer
Cataracts
Blindness
267
Give one danger of x-rays/gamma rays
Mutation of the genes
268
Describe the average power absorption and radiation for an object of constant temperature
Equal absorption and radiation
269
What kind of current is used to generate radio waves in an antenna?
Alternating current
