Waves Flashcards
1
Q
What is a wave?
A
Disturbance caused by oscillating source that transfers energy & info in the direction of wave travel, without transferring matter
2
Q
What is amplitude?
A
Wave’s maximum disturbance from its undisturbed position
3
Q
Illustrate amplitude on a wave
A
4
Q
What is wavelength?
A
Distance between the same point on two adjacent waves
5
Q
Illustrate wavelength on a wave
A
6
Q
What is frequency?
A
Number of complete waves passing a certain point per second
7
Q
What is frequency measured in?
A
Measured in hertz (Hz)
8
Q
What does 1 Hz mean?
A
1 Hz is 1 wave per second
9
Q
In transverse waves, what are oscillations (vibrations) like?
A
Oscillations (vibrations) are perpendicular (at 90°) to direction of energy transfer
10
Q
Give 3 examples of waves that are transverse
A
- All electromagnetic waves e.g. Light
- Ripples and waves in water
- A wave on a string
11
Q
In longitudinal waves, what are oscillations (vibrations) like?
A
Oscillations are parallel to the direction of energy transfer
12
Q
Give 2 examples of longitudinal waves
A
- Sound waves in air e.g. Ultrasound
- Shock waves e.g. Some seismic waves
13
Q
Longitudinal waves have areas of ______ and ______
A
Compression and rarefraction
14
Q
Sound waves are _______ and ________ waves
A
longitudinal and mechanical waves
15
Q
What is wave speed?
A
The speed at which energy is being transferred (or speed wave is moving at)
16
Q
All waves can be ______, ______ or ______ at the boundary between two different materials
A
Absorbed, Transmitted or Reflected
17
Q
When waves are absorbed by material, what happens (energy wise)?
A
Energy is transferred into material’s energy store (e.g. How microwaves work)
18
Q
What is meant when waves are transmitted?
A
Waves carry on travelling through new material - often leads to refraction
19
Q
What is a period of a wave?
A
Amount of time it takes for a full cycle of the wave to pass a point
20
Q
What is a wave front?
A
Is the locus of points in the same phase
21
Q
Why can waves undergo refraction?
A
Due to a change in wavelength
22
Q
What is the rule for all reflected waves?
A
Angle of incidence = Angle of reflection
23
Q
What is the angle of incidence?
A
Angle between incoming wave and the normal
24
Q
What is the angle of reflection?
A
Angle between reflected wave and the normal
25
What is the normal?
An imaginary line that's perpendicular to the surface at the point of incidence (point where wave hits boundary)
26
When is a wave refracted?
When wave crosses boundary between materials at an angle, it changes direction
27
How much a wave refracts depends on...
* How much the wave speeds up or slows down
* Which depends on density of two materials
28
The higher density of material = _____ wave travels through it
slower
29
When wave crosses a boundary and slows down, it bends _____ the normal
Slow = TOWARDS the normal
30
When wave crosses a boundary and speeds up, it bends _____ \_\_\_ the normal
fast = AWAY from the normal
31
What changes when a wave refracts?
Wavelength of wave
32
What stays the same when a wave refracts?
Frequency stays the same
33
What will happen if a wave travels along the normal?
It will change speed but NOT be refracted
34
What is the optical density of material?
A measure of how quickly light can travel through it
35
Higher optical density = ....
slower light waves travel through it
36
Describe how you can construct a ray diagram to show refraction with an aid of a diagram
1. Draw boundary line & normal (90° to boundary)
2. Draw incident ray that meets normal at boundary + angle of incidence
3. Draw refracted ray on other side of boundary
1. If 2nd material is more opictially dense than 1st = angle of refraction \< angle of incidence
2. If 2nd material is less opictially dense than 1st = angle of refraction \> angle of incidence
37
What is diffraction?
Spreading of waves when they pass through (narrow) gap or move past (edge of) obstacle
38
When does diffraction take place?
When wavelength of wave is comparable to size of obstacle or gap
39
Waves passing through gap/past edge of obstacle spread out without changing their... (name 3 things)
* Wavelength
* Speed
* Frequency
40
Wider gap = ...
less waves spread out (the smaller the diffraction)
41
Narrower gap = ...
more the waves spread out (the greater the diffraction)
42
Illustrate diffraction of waves through a wide gap
43
Illustrate diffraction of waves through a narrow gap
44
Illustrate diffraction of waves at an edge
45
Name 3 real life examples of where diffraction is used
* Optical instruments
* Ultrasound waves in medicine
* Radio wave reception
46
Explain how ultrasound waves in medicine work
Spread out from hand-held transmitter & reflect from tissue
boundaries inside womb
47
What happens if the transmitter is too narrow?
Waves spread out too much = image becomes too faint
48
What are narrow telescopes for?
Closer stuff
49
Explain how diffraction is used in the Hubble Space Telescope
1. Small amount of light passes through Hubble Space Telescope = small amount of diffraction occurs
2. Because telescope is so wide
3. Images are clear and detailed
50
Why do people who in hilly areas have poor TV reception?
Radio waves passing top of hill are diffracted by hill but they don't spread enough behind the toll
51
What are electromagnetic waves?
Transverse waves → transfer energy from a source to an absorber
52
All EM waves travel at the ____ \_\_\_\_\_\_ through ___ or \_\_\_\_\_
Travel at the same speed through air or vacuum (space)
53
EM waves form _____ \_\_\_\_\_\_\_ over a range of \_\_\_\_\_\_\_\_\_
continuous spectrum over a range of frequencies
54
How are EM waves grouped? (3x)
Based on their wavelength, frequency and energy
55
Recite the order of EM waves within the spectrum (from low freq. to high freq.)
56
What do the wavelengths of the electromagnetic spectrum range from?
10-15 m to 104 m and beyond
57
Why is there such a large range of frequencies of EM waves?
Because EM waves are generated by a variety of charges in atoms and their nuclei
58
Shorter wavelength = ....
higher its frequency = higher the energy
59
How is visible light detected?
By our eyes
60
How do we see the different wavelengths of visible light as?
As different colours
61
What 4 EM waves are used for communication?
* Radio waves
* Microwaves
* Infrared
* Visible Light
62
What are radio waves?
EM radiation - wavelength longer than 10 cm
63
Why can long-wave radio waves (1-10 km) be transmitted from e.g. London to halfway round world?
Because long wavelengths diffract (bend) around curved Earth surface i.e. they can diffract around hills, into tunnels, etc.
∴ Radio signals can be received even if receiver isn't in line of
the sight of transmitter
64
Why can short-wave radio signals (10m-100m) be received long
distances from a transmitter?
Because they're reflected from the ionosphere
65
How does Bluetooth work?
Uses short-wave radio waves to send data over short distance between devices without wires
66
Medium-wave signals (shorter ones) can relate from ionosphere depending on _______ \_\_\_\_\_\_\_\_ and ____ of day
depending on atmospheric conditions and time of day
67
What kind of wavelength do radio waves that are used for TV and FM radio transmissions have?
Very short wavelengths
68
To get reception why must TV and FM radio transmissions signals be in direct sight of the transmitter?
Signal doesn't bend or travel far though buildings
69
Name 3 uses of radio waves
* TV
* Radio Systems
* Bluetooth
70
Name 2 uses of microwaves
* Mobile phones
* Satellite television systems
71
Why does communication to and from satellites use microwaves?
They can easily pass through earth's watery atmosphere
72
Why is there a slight time delay between signal being sent and received?
∵ of long distance signal has to travel
73
Why are microwaves used to beam signals from one place to another and not radio waves?
∵ they don't spread as much as radio waves
74
Name 3 uses of infrared
* TV remote controls
* Night vision devices
* Heating
75
What does absorbing IR radiation cause objects to get?
Hotter
76
How can food can be cooked using IR radiation?
Temperature of food increases when it absorbs IR radiation
77
What does every object do (regarding IR radiation)?
They absorb and emit infrared radiation
78
Why do all objects emit IR radiation?
∵ of motion of their particles
79
Hotter object is = more ...
IR it radiates in given time
80
What does the amount and frequency of emitted raditation depend on?
Temperature and surface of object
81
What do objects at constant temperature do?
Emit IR radiation at same rate that they absorb it
82
What does an object that's hotter than its surroundings do?
Emits more IR radiation \> than it absorbs as it cools down
83
What does an object that's cooler than its surroundings do?
Absorbs more IR radiation \> than it emits as it warms up
84
Dark, matt surfaces are ___ \_\_\_\_ and ___ \_\_\_\_ of infrared radiation
good absorbers and good emitters
85
Light, shiny surfaces are ____ \_\_\_\_\_\_ and ___ \_\_\_\_\_ of infrared radiation
poor absorbers and poor emitters
86
Light, shiny surfaces are ___ \_\_\_\_\_\_\_ of infrared radiation
good reflectors
87
As an object heats up, what does it do?
Radiates more infrared radiation, at higher frequencies
88
What is black-body radiation?
Range of electromagnetic radiation emitted by an object at a particular temperature
89
What is a perfect black body?
Object that absorbs all of radiation that hits it, no radiation is transmitted or reflected
90
What happens if the atmosphere absorbs more radiation without emitting same amount?
Overall temperature will rise until absorption and emission are equal (global warming)
91
Name 2 uses of visible light
* Fibre optic communications
* Photography
92
What are optic fibres?
Thin glass or plastic fibres that carry data over long distances as pulses of visible light
93
How do fibre optic cables use visible light to transmit data?
* Work because of reflection → light rays are bounced back and forth until they reach end of fibre
* Light is not easily absorbed or scattered as it travels along fibre
94
Name 2 uses of UV
* Security pens
* Artificial tans
95
How does security marking work?
* Security pens → mark property with name
* Under UV light ink will glow (fluoresce) but it's invisible otherwise
* Helps police identify your property if it's stolen
96
What are X-rays used for?
Medical imaging - to see if a person has broken bones
97
How do X-rays work?
* X-rays transmit easily through flesh but very easily through denser material like bones/metal
* Starts off as white
* White = x-rays absorbed
* Black = x-rays transmitted
98
Name 2 uses of gamma rays
* Sterilising surgical instruments
* Killing harmful bacteria in food
99
What is the problem with low energy waves?
Have a heating effect
100
What is the problem with high energy waves?
Have enough energy to cause ionisation
101
What is the danger of microwaves?
Heating of body tissue
102
What is the danger of infrared?
Skin burns
103
What are the dangers of ultraviolet? Name 2
Skin cancer and blindness
104
What is the danger of X-rays?
High doses kill cells
105
What is the danger of gamma rays?
Genetic mutations
106
What radiographers do to protect themselves from the effects of gamma rays/x-rays?
107
X-rays affect a photographic lm in the same way as \_\_\_\_
light
108
Name 4 things X-rays are used in
* CT scanning
* Bone fractures
* Dental problems
* Killing cancer cells
109
How can X-rays and gamma rays be used to treat people with cancer?
∵ high doses of these rays kill all living cells → they're carefully directed towards cancer cell
110
Why is gamma radiation used as medical tracer?
Can pass out through body to be detected
111
What are sound waves?
Longitudinal waves and cause vibrations in medium, which are detected as sound
112
Why can't sound waves travel in space?
There's no particles to move/vibrate
113
What is the range of human hearing?
20 Hz to 20 000 Hz
114
How is the pitch of sound determined?
By frequency of vibrations of source
115
How is the loudness of sound determined?
Size of amplitude of disturbance
116
Sounds can \_\_\_\_, _____ & \_\_\_\_
Reflect, refract and diffract
117
What reflects sound waves?
Hard flat surfaces
118
What are echoes essentially?
Reflected sound waves
119
What is ultrasound?
Ultrasound is a sound with frequencies higher than 20 000 Hz
120
Explain how electronic systems can be used to produce ultrasound
1. Electrical devices can produce electrical oscillations of any frequency
2. Then conserved into mechanical vibrations to produce sound waves beyond range of human hearing
121
Ultrasound waves get ____ \_\_\_\_\_\_\_ at boundaries between two different media
partially reflected
122
What is meant by partial reflection?
When wave passes from 1 medium into another:
* Some of wave reflected off boundary
* & some is transmitted (and refracted)
123
How can we use the partial reflection in ultrasound?
Time taken for reflections to reach a detector can be used to measure how far away boundary is
124
Name 3 uses of ultrasound
* Prenatal scanning
* Removal of kidney stones
* Finding flaws in objects (like pipes or materials)
125
Explain how ultrasound can be used in prenatal scanning
1. Ultrasound waves → pass through body but when reach boundary between two different media (e.g. fluid in womb and skin of foetus) = some of wave reflected back & detected
2. Exact timing + distribution of these echoes → processed by computer
* → produces video image of foetus
126
Explain how ultrasound can be used in finding flaws in objects like pipes or materials
1. Ultrasound waves entering material → reflected by far side of material
2. If there's flaw (e.g. Crack inside object) = wave will be reflected sooner
127
What can CT scans do?
Distinguish between different types of soft tissue as well as between bone and soft tissue
128
Explain how CT scans work
1. Take range of X-ray images from various position
2. → processed by computer to build 3D image of inside of patient's body
129
Name 3 pros of CT scans
1. Lets doctor gain much greater insight into what's wrong with patient
1. Only method that provides detailed images of bone, soft tissue, blood vessels
2. Painless
3. Widely available
130
Name 3 cons of CT scans
1. Exposure to radiation
2. Allergic reaction to contrast material
3. Misinterpreted test results
131
How can you can measure risk of radiation?
Using Radiation Dose in Sieverts
132
What does risk depend on?
Total amount of radiation absorbed and how harmful the type of radiation is
133
How is ultrasound used remove kidney stones?
1. Powerful ultrasound waves used to break kidney stone into bits
2. Fragments are then small enough to leave kidney naturally
134
When something moves towards you, what happens to the wavelength and frequency of sound?
Wavelength decreases and frequency increases
135
When something moves towards you, what happens to the pitch of sound?
Becomes higher
136
When something moves away from you, what happens to the wavelength and frequency of sound?
Wavelength increases and frequency decreases
137
When something moves away from you, what happens to the pitch of sound?
Becomes lower
138
What an image produced in a plane mirror like? (name 3 things)
* Virtual
* Upright
* Laterally inverted
139
What can the refraction by a prism lead to? (2x)
Dispersion of light waves and formation of a spectrum
140
When does total internal reflection occur?
Angle of incidence in denser medium \> critical angle
141
How is visible light and infrared transmitted through optical fibre via?
Total internal reflection
142
What are optical fibres used for? (2x)
* Communication technology
* Medicine e.g. endoscope
143
What is an endoscope used for?
To see inside body cavity without cutting body open
144
Explain how an endoscope works
1. Contains 2 bundles of optical fibres
1. Used to shine light into cavity
2. Transmit light back so surgeon can see internal surface of cavity
* Tiny lens = image at the end of fibres (seen directly or using camera)
145
Name 2 benefits of optical fibres
1. Can carry more info than ordinary cable of same thickness
2. Signals in optical fibres don't weaken as much over long distances as signals in ordinary cables
1. Don't need to be amplified as often as signals in copper cables
146
How does a lens form an image?
By refracting light
147
What happens to light in a convex lens?
Bulges outwards - causes rays of light parallel to axis to be brought together (converge) at principal focus
148
What happens to light in a concave lens?
Cave inwards - causes rays of light parallel to axis to spread out (diverge)
149
What is the focal length?
Distance form centre of lens to principal focus
150
To describe an image properly, what are the 3 things you need to say?
1. How big it is compared to object
2. Whether it's upright or inverted (upside down) relative to object
3. Whether it's real or virtual
151
What is a real image?
Where light from an object comes together to form an image on a 'screen' (e.g. eye's retina)
152
What is a virtual image?
When rays are diverging so light from the object appears to be coming from a completely different place
153
Give 2 examples of virtual image
* Image of your face in a mirror
* Image gottenvwhen looking at an object through a magnifying lens
154
What type of lens do magnifying glasses use?
Convex Lenses
155
Object being magnified must be _____ to lens than the ____ length
Closer to lens than the focal length
156
What's a useful pharse to use in exam if they ask you about virtual images?
"you can't project a virtual image onto a screen"
157
Name 7 parts of the eye
* retina
* variable focus lens
* cornea
* pupil
* iris
* ciliary muscle
* suspensory ligaments
158
What is the retina?
Light sensitive cells at back of your eye
159
What is the function of the retina?
Where lens will focus light rays from object and real image will be formed
160
What's the function of the variable focus lens?
Focuses light into retina
161
What's the function of the cornea and what is it?
Transparent layer that protects eye & helps to focus light into retina
162
What's the function of the pupil and what is it?
Central hole formed by iris - light enter eye through pupil
163
What's the function of the iris and what is it?
Coloured ring of muscle that controls amount of light that can enter eye
164
What is the function of ciliary muscles?
Causes changes in shape of lens = allow light to be focused arriving from varying distances
165
What do the suspensory ligaments do?
Attach ciliary muscles to the lens
166
Light entering the eye is refracted by what?
Cornea & Lens
167
What is usually the near point of a human eye?
Approximately 25 cm from the eye
168
What is usually the far point of a human eye?
Infinity from the eye
169
What can the eye focus on? (objects between...)
Objects between near point and far point
170
What meant by the range of vision?
Distance between the near point and far point
171
What is long-sightedness caused by?
Eyeball being too short OR eye lens being unable to focus a sharp image on the retina
172
What is short-sightedness caused by?
By eyeball being too long OR eye lens being unable to focus a sharp image on the retina
173
Where does long-sightedness cause the image to form?
Behind retina
174
Where does short-sightedness cause the image to form?
Before retina
175
How can long-sightedness be corrected?
By using a convex (convering) lens
176
How does a convex lens correct long-sightedness?
Causes light rays to converge slightly before they hit lens = they refract perfectly onto retina
177
How can short-sightedness be corrected?
With concave (diverging) lens
178
How does a concave lens correct long-sightedness?
Light rays diffract outwards slightly as they pass lens = focused exactly on retina by lens in eye
179
What are lasers?
Concentrated sources of light
180
Name 3 uses of lasers
Cutting, cauterising and burning
181
Why are lasers used in eye surgery?
To correct visual defects
182
In the eye, the image is brought to focus on retina by changing the shape of the lens. What is the camera equivalent?
Image is brought to focus on film or CCD sensor by varying the distance between flim and lens
183
What is the camera equivalent of the retina?
Film or CCD sensor
