Waves Flashcards
1
Q
What is a wave?
A
A vibration that transfers energy without transferring matter
2
Q
What is a transverse wave?
A
A wave where the oscillations are perpendicular to the direction of energy transfer of the wave
3
Q
What is a longitudinal wave?
A
A wave where the oscillations are parallel to the direction of energy transfer of the wave
4
Q
What happens when waves travel through a medium?
A
The particles vibrate and transfer energy between each other but they stay in the same place
5
Q
What are crests and troughs?
A
Points of maximum positive and maximum negative displacement from the particles rest position
6
Q
What is the amplitude of a wave?
A
The maximum displacement of a point from its undisturbed position
7
Q
What is the equation for the period of a wave?
A
Period= 1 over frequency.
8
Q
What is the wavelength?
A
The distance between the same point on two adjacent waves.
9
Q
What is the frequency?
A
The number of complete waves passing a certain point per second.
10
Q
What is frequency measured in?
A
Hertz (Hz)
11
Q
How can the speed of sound be measured using an oscilloscope?
A
Set up oscilloscope so the detected waves at each microphone as shown as separate waves, slowly move microphones away until two waves are aligned, measure distance between microphones to find wavelength then use formula
12
Q
What can happen when waves arrive at a boundary between two different materials?
A
They can be absorbed by the material they are trying to pass into, they can be transmitted and keep on travelling (often leading to refraction) or they can be reflected
13
Q
What is the rule for all reflected waves?
A
Angle of incidence = angle of reflection
14
Q
What is the angle of incidence?
A
The angle between the incoming wave and the normal
15
Q
What is the angle of reflection?
A
The angle between the reflected wave and the normal
16
Q
What is the normal?
A
An imaginary line that’s perpendicular to the surface at the point of incidence, normally shown as a dotted line
17
Q
What is specular reflection?
A
When a wave is reflected in a single direction by a smooth surface
18
Q
What is diffuse reflection?
A
When a wave is reflected by a rough surface and the reflected rays are scattered in lots of different directions
19
Q
Why does diffuse reflection happen?
A
Because the normal is different for each incoming ray, which means that the angle of incidence is different for each ray
20
Q
What are EM waves?
A
Waves that are transverse and transfer energy from a source to an absorber and all travel at the same speed through air or a vacuum
21
Q
Give the EM spectrum, with each wave increasing frequency and decreasing wavelength
A
Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays
22
Q
Why are there such a large range of frequencies in the EM spectrum?
A
Because EM waves are generated by a variety of changes in atoms and their nuclei
23
Q
What is refraction?
A
When a wave crosses a boundary between materials at an angle and it changes direction
24
Q
What does how much a wave refracts depend on?
A
How much the wave speeds up or slows down, which depends on the density of the two materials
25
How does speed affect a wave when crossing a boundary?
If it slows down it will bend towards the normal and if it speeds up it will bend away from the normal
26
How is wavelength and frequency affected when a wave is refracted?
Wavelength changes but frequency stays the same
27
What is the optical density of a material?
A measure of how quickly light can travel through it; the higher the optical density, the slower light waves travel through it
28
How do you construct a ray diagram for a refracted ray of light?
Draw a horizontal boundary, then draw the normal perpendicular to it, draw an incident ray that meets the normal at the boundary, then draw the refracted ray on the other side of the boundary.
29
How does the optical density affect the size of the angle of refraction in comparison to the size of the angle of incidence?
If the second material is optically denser than the first, the refracted ray bends towards the normal and the angle of refraction will be smaller than the angle of incidence
30
What are EM waves made up of?
Oscillating electric and magnetic fields
31
How are radio waves produced by an alternating current in an electrical circuit?
When transmitted radio waves reach a receiver, they are absorbed, the energy carried by the waves is transferred to the electron sin the material of the receiver, causing the electrons to oscillate, generating an alternating current which has the same frequency as the radio wave that generated
32
How long are the wavelegnths of radio waves?
Around 10 cm or longer
33
Why can long-wave radio be transmitted around the world?
The longer wavelengths diffract around the curved surface of the earth, as well as diffracting around things like hills or into tunnels
34
Why can short-wave radio signals be received at long distances away from the transmitter?
They are reflected from the ionosphere (an electrically charged layer in the earth's upper atmosphere)
35
How does satellite TV work (in terms of waves)?
Microwaves are set from a transmitter on earth into space, where they are picked up by a satellite orbiting above earth. The satellite transmits the signal back to earth in a different direction whee it is received by a satellite dish on the ground
36
How do microwave ovens work?
The microwaves penetrate a few centimetres into the food before being absorbed and transferring the energy they are carrying to the water molecules in the food, causing the water to heat up, which cooks the rest of the food
37
What uses does infrared radiation have?
Infrared cameras (which detects the IR radiation and turns it into an electric signal) , cooking food as absorbing IR radiation causes an object to get hotter and electric heaters which emit IR radiation
38
How do fibre optic cables work?
Visible light rays are bounced back and forth until they reach the end of the fibre. The light is not easily absorbed or scattered as it travels along a fibre
39
Why do fluorescent colours look so bright?
Fluorescence is a property of certain chemicals, where UV radiation is absorbed and then visible light is emitted
40
What are the uses of UV radiation?
Fluorescent lights (same as colours except the visible light is radiated out by a layer as phosphorus), security pens which only show up under UV, suntans (from the sun) and UV lamps
41
How do X-rays produce an image of bones in a body?
They easily pass through flesh but not bones so the amount of radiation that is absorbed can allow you to build up an image
42
How are X-rays and gamma rays sued to treat cancer?
High doses of these rays can kill all living cells, so they are carefully directed towards the cancer cells to avoid killing healthy cells
43
Why is gamma radiation a good medical tracer?
It can pass out through the body to be detected
44
How to radiographers keep their exposure to X-rays and gamma rays to a minimum?
They wear lead aprons and stand behind lead screen or leave the room
45
What types of waves can harm people and why?
High frequency waves as they transfer a lot of energy. This includes UV which damages surface cells (sunburn and aging), X-rays and gamma rays which both are ionising radiation (causing gene mutation or cell destruction)
46
What is radiation dose?
A measure of the risk or harm from the body being exposed to radiation, which is measured in sieverts or millisieverts
47
What is a convex lens?
A lens which bulges outward, causing rays of light parallel to the axis to be brought together at the principal focus
48
What is a concave lens?
A lens that caves inwards, causing parallel rays of light to spread out
49
What is the axis of a lens?
A line passing through the middle of the lens
50
What is the principal focus of a convex lens?
Where rays hitting the lens parallel to the axis all meet
51
What is the principal focus of a concave lens?
The point where rays hitting the lens parallel to the axis appear to all come from (behind the lens)
52
What is the focal length?
The distance from the centre of the lens to the principal focus
53
What are the three rules for refraction in an convex lens?
An incident ray parallel to the axis refracts through the lens and passes through the principal focus on the other side
An incident ray passing through the principal focus refracts through the lens and travels parallel to the axis
An incidence tray passing through the centre of the lens carries on in the same direction
54
What are the three rules for refraction in a concave lens?
An incident ray parallel to the axis refracts through the lens, and travels in line with the principal focus
An incident ray passing through the lens towards the principal focus refracts through the lens and travels parallel to the axis
An incident ray passing through the centre of the lens carries on in the same direction
55
What is a real image?
Where the light from an object comes together to form an image on a 'screen' (like an image formed on the eye's retina)
56
What is a virtual image?
Where the rays are diverging, so the light from the object appears to be coming from a completely different place (e.g. looking in a mirror or magnifying glass)
57
What three things do you need to do to describe an image properly?
How big it is compared to the object, whether it is upright or inverted compared to the object and whether it is real or virtual
58
How do you draw a ray diagram for an image through a convex lens?
Pick a point at the top of the object, then draw an ray going from the object to the lens parallel to the axis of the lens, draw another ray from the top of the object going through the middle of the lens, draw a refracted ray passing through the principal focus, mark where the rays meet (at the top) then repeat the process for a point at the bottom
59
How do you draw a ray diagram for an image through a convex lens?
Pick a point at the top of an object, draw a ray going from the object to the lens parallel to the axis, draw another ray from the top of the object going right through the middle of the lens, draw ray from the principal focus, make it dotted before it reaches the lens, mark where the refracted meet, then repeat the process for a point on the bottom of the object
60
What do concave lenses always create?
A virtual image: the image is right way up, smaller than the object and on the same side of the lens as the object
61
How do magnifying glasses work?
By creating a magnified virtual image
62
Give the magnification formula
magnification = image height / object height
63
What is a primary colour?
Colours that can't be made by mixing any other colours together: red, green and blue
64
What are opaque objects?
Objects that do not transmit light: when visible light waves hit them, they absorb some wavelengths of light and reflect others
65
What does the colour of an opaque object depend upon?
It depends upon which wavelengths of light are most strongly reflected. If it is not a primary colour, it may be reflecting either the wavelengths of light corresponding to that colour or the wavelengths of the primary colours that can mix together to make that colour
66
How do white and black objects reflect light?
White objects reflect all of the wavelengths of visible light equally and black objects absorb all wavelengths of visible light; your eyes see black as the lack of any visible light
67
What is a translucent or transparent object?
They are objects that transmit light. Some wavelengths of light may be absorbed or reflected; the object's colour is related to the wavelengths of light transmitted and reflected by it
68
How do colour filters work?
They filter out different wavelengths so that only certain colours (wavelengths) are transmitted so the rest are absorbed
69
What is a primary colour filter?
A colour filter that only transmits that colour e.g. is white light was shone at a blue colour filter, only blue light would be let through
70
How do colour filters work that aren't for primary colours?
They let through both the wavelengths of light for that colour and the wavelengths of the primary colours that can be added together to make that colour
71
Which objects emit and absorb IR?
All objects; IR is emitted form the surface of an object
72
How much IR radiation does an object hotter or colder than it's surroundings emit?
A hotter object emits more IR radiation than it absorbs as it cools down whereas a colder object absorbs more than it emits as it warms up
73
How much IR radiation is absorbed and emitted by an object at a constant temperature?
It emits infrared radiation at the same rate that it is absorbing it
74
Which types of surfaces are better at absorbing and emitting IR?
Black and matt surfaces
75
What is a Leslie cube?
A hollow, watertight metal cube whose four vertical faces have different surfaces
76
What is a perfect black body?
An object that absorbs all radiation that hits it; no radiation is reflected or transmitted. A perfect black body is the best possible emitter of radiation
77
What does the intensity and distribution of the wavelengths emitted by an object depend on?
The object's temperature; intensity is the power per unit area. AS temperature increases, so does intensity, however, the intensity increases more rapidly than longer wavelengths, causing the peak wavelength to decrease
78
What does the overall temperature of the earth depend on?
The amount of radiation is reflects, absorbs and emits
79
Why does the overall temperature of the earth stay fairly constant?
During the day, there is an increase in temperature as lots of radiation is transferred to the earth from the sun and absorbed but at night, the temperature decrease as less radiation is being absorbed than emitted
80
Why do changes to the atmosphere cause a change to the earth's overall temperature?
If the atmosphere starts to absorb more radiation without emitting the same amount, the overall temperature will rise until absorption and emission are equal again (global warming)
81
What are sound waves causes by?
Vibrating objects: these vibrations are passed through the surrounding medium as a series of compressions are rerefractions
82
What medium do sound waves travel fastest in and why?
Solids as it is easier for the particles to pass the vibrations to one another
83
Why can't sound waves travel in space?
It is a vacuum, meaning that there are no particles to vibrate
84
How does the human ear hear sound?
Sound waves that reach the ear drum cause it vibrate, vibrations are passed on to tiny bones called ossicles, through the semicircular canals and to the cochlea, cochlea turns these into electrical signals, get sent to brain and allow you to sense the sound
85
What frequencies can humans hear?
Anything in the range of 20 Hz - 20 kHz
86
What is human hearing limited by?
The size and shape of the ear drum as well as the structure of all the parts within the ear that vibrate to transfer the energy from the sound wave
87
What are echoes?
Sound waves reflected by hard, flat surfaces
88
How is speed affected when a sound wave enters a denser material and why?
The sound wave speeds up because when a wave travels into a different medium, it's wavelength changes but it's frequency remains the same so it's speed must also change
89
How is ultrasound created?
Electrical devices can be made to produce electrical oscillations over a range of frequencies. These can easily be converted into mechanical vibrations to produce sound waves beyond the range of human hearing
90
What is partial reflection?
When a wave passes from one medium to another, some of the wave is reflected off the boundary between the two media and some is transmitted
91
How can ultrasound be used to measure how far away a boundary is?
When you point a pulse of ultrasound at an object, wherever there are boundaries, some of the ultrasound gets reflected back. The time it takes for the reflections to reach a detector can be used to measure the distance
92
How is ultrasound used in medical imaging?
Ultrasound waves can pass through the body, but whenever they reach a boundary between two different media, some of the wave is reflected back and detected. The exact timing and distribution of these echoes are processed by a computer to produce a video image of the foetus.
93
How is ultrasound used in industrial imaging?
Ultrasound waves can be used to find flaws in material. When entering a material, they will usually be reflected by the far side of the material. If there is a flaw (a crack) inside the object, the wave will be reflected sooner
94
How are seismic waves produced and detected?
They are caused by an earthquake somewhere and can be detected by seisometers
95
What do seismologists measure?
The time it takes for the shock waves to reach the seisometers and which parts of earth don't receive the shock waves at all
96
What happens if a seismic wave reaches a boundary?
Some waves will be refracted and some will be absorbed. If the waves are refracted, they change speed gradually, resulting in a curved path, but if the properties change abruptly, the wave speed changes abruptly, resulting in a path with a kink
97
What are the two types of seismic waves?
P waves and S waves
98
Describe P waves
They are longitudinal, travel through solids and liquids and are faster than S waves
99
Describe S waves
They are transverse and can't travel through liquids or gases. They're slower than S waves
100
What can observing how seismic waves are absorbed and refracted tell scientists?
They can work out where the properties of earth change dramatically, helping scientists to build up the internal structure of the earth
