P13 - Electromagnetic Waves Flashcards
(86 cards)
1
Q
What are Carrier waves?
A
Waves used to carry any type of signal
2
Q
What is a charge-coupled device (CCD)?
A
An electronic device that creates an electronic signal from an optical image formed on the CCD’s array of pixels
3
Q
What is a contrast medium?
A
An X-ray absorbing substance used to fill a body organ so the organ can be seen on a radiograph
4
Q
What is the electromagnetic spectrum?
A
The continuous spectrum of electromagnetic waves
5
Q
What is ionisiation?
A
The process by which atoms become charged
6
Q
What are microwaves?
A
Electromagnetic waves between infrared radiation and radio waves in the electromagnetic spectrum
7
Q
What is an optical fibre?
A
Thin glass fibre used to transmit light signals
8
Q
What is a radiation dose?
A
Amount of ionising radiation that a person receives
9
Q
What is a radiowave?
A
Electromagnetic waves of wavelengths greater than 0.1m
10
Q
What is Ultraviolet Radiations (UV)?
A
electromagnetic waves between visible light and X-rays in the electromagnetic spectrum
11
Q
What is wave speed?
A
The distance travelled per second by a wave crest or trough
12
Q
What is white light?
A
Light that includes all colours of the spectrum
13
Q
What is the structure of an electromagnetic wave?
A
Electromagnetic waves are transverse waves that transfer energy. The vibrations come in the form of electric and magnetic fields that make up the EM wave. They oscillate 90* to the direction in which the wave is travelling (The electric field also oscillates 90* to the magnetic field).
14
Q
What is are the properties of an electromagnetic wave?
A
- They are transverse waves.
- They can travel through a vacuum (they do not require a medium to travel through).
- They travel at the speed of light
- EM waves with a high frequency have high energy, while low frequency waves have low energy
- They form a continuous spectrum
15
Q
What is an electromagnetic wave?
A
Electrical and magnetic disturbances that transfer energy from one place to another
16
Q
What is the order of the EM spectrum (from long wavelength to short) (low frequency to high)
A
Radio Waves Microwaves Infrared Visible Light Ultraviolet Light X-rays Gamma radiation
17
Q
What is the speed of light in a vacuum?
A
3.0x10^8
18
Q
What is the equation for the speed of a wave?
A
Wave speed = Frequency x wavelength
19
Q
If a shiny white can of water and a matt black can of water are both heated by an infrared lamp, which will heat quickest?
A
The water in the black beaker will increase in temperature more than the temperature of the water in the white beaker. This is because matt, dark surfaces absorb more infrared radiation than shiny, light surfaces
20
Q
What emits more infrared radiation, a shiny white surface or a matt black surface?
A
matt black surface, dark matt surfaces are good emitters of infrared radiation whereas white shiny surfaces are poor emitters of infrared radiation
21
Q
What absorbs more infrared radiation, a shiny white surface or a matt black surface?
A
matt black surface, dark matt surfaces are good absorbers of infrared radiation whereas white shiny surfaces are poor absorbers of infrared radiation
22
Q
If a matt black can and a white shiny can where both filled with hot water, which volume of water would be hottest after 5 minutes?
A
The water in the shiny white can would be hottest, this is because a shiny white surface is a poor emitter of infrared radiation
23
Q
What are the properties of a short wavelength carrier wave?
A
- More information carried
- More energy carried
- Shorter range (greater absorption by the atmosphere)
- The less they spread out
24
Q
What are the properties of a long wavelength carrier wave?
A
- Less information carried
- Less energy carried
- Greater range (less absorption by the atmosphere)
- The more they spread out
25
What can Ultraviolet light be used for?
* Sun beds
* Fluorescent materials
* Security
* Sterilisation
26
How can Ultraviolet light be used with fluorescent materials?
Fluorescent materials absorb UV light and re-emit the energy as visible light. This has uses in fluorescent paint and fluorescent light bulbs (really energy efficient)
27
How can UV light be used in security?
Some types of ink are invisible until UV light is shined on it. They absorb the UV light and re-emit it as visible light. This can be used to mark valuable objects or money
28
How can UV light be used in sterilisation?
UV light destroys microorganisms
29
What are the 3 types of ionising radiation?
* UV Light
* X-rays
* Gamma radiation
30
What are the dangers of UV light?
UV light has a shorter wavelength than visible light, this means that it carries more energy and can be damaging:
* They are harmful to human eyes and may cause blindness
* They are harmful to your skin, too much UV light from the sun or a tanning bed may age the skin prematurely, cause sunburn, and as it is ionising it may cause skin cancer
31
How can you protect yourself from the dangers of UV light?
* If you stay outdoors during the summer, use skin creams to block UV waves and prevent them reaching your skin
* Do not look directly at the sun or other sources of UV light
* Do not go over the recommended time in a tanning bed and do wear protective goggles
32
How are X-rays produced?
X-rays are produced when electrons or other particles travelling at high speeds are stopped. X-ray tubes are used to produce X-rays
33
How are gamma rays produced?
Gamma rays are produced when unstable nuclei in radioactive substances decay and release energy in the form of EM waves
34
What are some similarities of X-rays and Gamma Rays?
* Very high frequency
* Very low wavelength
* High penetrating power
* Will be stopped by a thick lead plate
35
Describe the penetrating power of Gamma rays and X-rays
Gamma rays and X-rays both are highly penetrating as they have short-wavelengths (therefore carry much more energy than longer wavelength EM waves). Gamma rays have shorter wavelengths than X-rays and are therefore more strongly penetrating
36
What does a white piece of clothing look like under a UV lamp?
It glows blue, this is because many cleaning detergents contain fluorescent dyes to make white clothes brighter.
37
What are the dangers of X-rays and Gamma radiation, and how do you protect against them?
They are highly penetrative and are also forms of ionising radiation. This means they may cause mutations in cells which may lead to a cancerous tumour forming. To protect against them you should wear a thick plate of lead
38
Describe how ionising radiation works?
High-frequency radiation (UV, X-ray, Gamma) can knock electrons out of a substance as it passes through. This process is known as ionisation. If it happens to the atoms of living cells it can damage the cell, causing mutation of genes and cancerous growth. At higher doses it can kill the cell
39
What is a CT scanner?
A CT scanner is a circular machine in which the patient sits inside, the x-ray moves around the inside of the ring and at each position x-rays are released to form an image
40
What are the advantages of a CT scanner?
* It can form a 3d image
| * It can distinguish between soft tissue
41
What are the disadvantages of a CT Scan?
* They are very expensive
| * A higher dose of ionising radiation is administered to the patient
42
How is an X-ray image produced?
When the X-ray tube is switched on, X-rays from the tube pass through the part of the patients body under investigation. X-rays pass through soft tissue, but they are absorbed by bones, teeth and metal objects. The parts of the film or detector that the X-rays reach become darker than the other parts. Therefore the bones appear lighter than the surrounding material (which appears dark). The radiograph shows a "negative image".
43
What does a hole or cavity in a tooth show up as in an X-ray?
A dark area in the bright image of the tooth
44
What are 2 advantages of using an X-ray?
* They can accurately show if bones are broken or teeth contain cavities
* They can be used to destroy cancerous tumours
45
What are 2 disadvantage of using X-rays?
* They are a form of ionising radiation, in high doses they may cause cancer
* They cannot distinguish between soft tissue
46
Why can UV waves be used to image organs and unborn babies?
Ultrasound waves are used to image unborn babies and organs inside the human body. This is because ultrasound waves are partially reflected at body organs. This is because body organs have a different density to surrounding tissue. This means some of the ultrasound waves are reflected and detected by the transducer and used to form an image.
47
What precautions are taken when using X-rays?
* People are limited in the number of X-rays they can receive
* A thick lead plate prevents radiations reaching healthy tissue during radiotherapy
* Shielded walls containing lead are built around the room
* Workers wear a thick lead apron
* Film badges are used to monitor radiation exposure
48
Describe one use of ultrasound for medical treatment (not medical imaging)
destruction of kidney stones
49
What is a source of a radio wave?
Radio waves re created when an alternating current in an electrical circuit creates an electromagnetic wave
50
What is the effect on the human body of a radiowave?
It passes straight through the body without being absorbed
51
What is 1 use of a radio wave?
It can be used to carry signals (they act as a carrier wave), this is because they have a long wavelength and therefore can travel very far
52
What is the effect on the human body of a microwave?
Some wavelengths of microwave can be absorbed, causing heating of cells, which may be dangerous
53
What is the source of infrared radiation?
All objects give off infrared radiation, the hotter the object, the more infrared radiation given off
54
What is the effect of infrared radiation on the human body?
It is mostly reflected or absorbed by the skin, causing heating. It may cause burns if too much is absorbed
55
What is the effect of visible light on the human body?
It is mainly reflected or absorbed, it may cause some slight heating effects
56
What is the effect on the human body of UV radiation?
UV radiation has a high frequency, so it transfers more energy, therefore causing more damage. It is ionising as it can knock electrons out of their shell. This damages cells which may cause genetic mutations and cancer.
57
What is the effect of x-rays on the human body?
UV radiation has a high frequency, so it transfers more energy, therefore causing more damage. It is ionising as it can knock electrons out of their shell. This damages cells which may cause genetic mutations and cancer.
58
What do waves not transfer?
Matter
59
What is the wavelength of visible light?
400nm to 700nm
60
What are the uses of infrared radiation?
* Optical Fibres
* Remote control handsets
* Infrared scanners and cameras
* Electric heaters and cookers
61
Why is Infrared radiation used in optical fibres?
Infrared radiation is absorbed less than visible light in the glass fibres, this means the information will not be lost
62
Why is infrared radiation used in remote control handsets?
Remote control handsets for TV transmit signals carried by Infrared radiation. When you press a button on the handset, it sends out a sequence of infrared pulses. infrared radiation is used as the infrared pulses can easily be produced and detected electronically
63
Why is infrared radiation used in scanners and cameras?
* Infrared scanners are used in medicine to detect infrared radiation emitted from hot spots on the body surface. These hot areas can mean the tissue beneath is unhealthy
* Infrared cameras can be used to see people, animals, and other hot objects in the dark
64
Why is infrared radiation used in electric heaters and electric cookers?
Infrared radiation is used to heat up objects quickly:
* Electric heaters emit infrared radiation to heat a room quickly
* Electric cookers have halogen hobs as halogen hobs heat up food much faster than conventional hobs. This is because halogen hobs are designed to emit much more infrared radiation than conventional hobs
65
What are the uses of microwaves?
* Communications
| * Heating food
66
Why are microwaves used for communications?
Microwaves are used for communications as they can pass through the atmosphere and reach satellites above the earth, they can also carry mobile phone signals. They do not spread out much and are therefore suitable to reach a satellite. The microwave signal is send my a transmitter, where it is received by a satellite receiver dish, the satellite then transmits the signal back towards earth in a different direction where it is received by a satellite dish
67
Why is a microwave used to heat food?
Microwave ovens heat food faster than ordinary ovens. This is because they can penetrate into the food and are absorbed by the water molecules in the food, heating it. The water molecules then transfer this energy to the food around it
68
Why does a microwave oven not become hot like the food that it is cooking?
Microwaves are absorbed by water molecules in the food. The oven itself does not contain any water molecules and therefore does not become hot
69
What are radio waves with a wavelength less than 1m used for?
Transferring signals between TV masts and a TV as they can carry much more energy than longer waves and do not need to travel as far
70
What are radio waves with a wave length greater than 100m used for?
National and international radio stations because they have a much longer range than short-wavelength radio waves
71
What is an alternating current?
a current that repeatedly reverses its direction
72
Explain how a radio wave transfers signals
An oscillator supplies carrier waves to the transmitter in the form of an alternating current.
The audio signal is supplied to the transmitter where it is used to modulate the carrier waves.
The modulated carrier waves from the transmitter are supplied to the transmitter aerial. The varying alternating current supplied to the aerial causes it to emit radio waves that carry the audio signal
When the radio waves are absorbed by the receiver aerial, they induce an alternating current in the receiver aerial, which causes oscillations in the receiver. The frequency of the oscillations is the same as the frequency of the radio waves
The receiver circuit separates the audio signal from the carrier waves. The audio signal is then supplied to a device that sneds out sound waves similar to that received by the microphone.
73
How does an optical fibre work?
optical fibres are very thin glass fibres. They are used to transmit signals carried by visible light or infrared radiation. The light rays cannot escape from the fibre as when they reach the surface of the fibre they are reflected back into the fibre. The light rays are continually reflected until they reach the end of the fibre (the light is not scattered or absorbed).
74
What are the advantages of optical fibre communication?
* Optical fibres carry much more information as the light has a much shorter wavelength than radio waves
* The optical fibres are more secure than radio waves as the signals always stay within the fibres
75
What are the uses of X-rays?
* Medical Imaging
* Radiotherapy
* Detection of internal cracks in metal objects
76
What are radiographs?
An imaging technique using radiation to produce images of internal human structures
77
Why are X-rays used to detect internal cracks in metal objects
The more dense an object is, the more X-rays it absorbs from an X-ray beam passing through it. This different amounts of X-rays received on the opposite side of the metal object can be used to detect if there is a crack inside the metal object
78
What are the uses of gamma radiation?
* Radiotherapy
* Sterilisation
* Radioactive tracers
79
What is a film badge and what does it do?
A device containing photographic film which registers the wearer's exposure to radiation. This allows the users exposure to radiation to be monitored
80
How can gamma radiation be used in sterilisation?
Gamma rays are extremely high energy. Exposing food to gamma rays kills 99% of disease-carrying bacteria and pathogens. They can also be used to sterilise and kill any harmful bacteria on medical instruments
81
How can gamma radiation be used in radioactive tracing?
A gamma emitting source is injected into the patient, and so its progress around the body is followed as the gamma rays exit the body and are detected outside
82
How can organs made from soft tissue be imaged using an X-ray?
The organ can be filled with a substance called a contrast medium that absorbs X-rays. This enables the interanl surfaces in the organ to be seen on the radiograph.
83
What is a flat-panel detector and what does it do?
A flat panel detector is a small screen that contains a Charge Coupled Device (CCD). The sensors in the CCD convert X-rays to light. The light rays then create electronic signals in the sensors that are sent to a computer, which displays a digital X-ray image
84
What does a radiation dose depend on?
* The type of radiation used
* How long the body is exposed to the radiation
* The energy per second absorbed by the body from the radiation
85
What is the unit for radiation dose?
Sieverts (Sv)
86
What is the difference between X-rays used in imaging and X-rays used in radiotherapy?
The X-rays used for therapy carry much more energy than the X-rays used for imaging. Low-energy X-rays are suitable for imaging because they are absorbed by bones and teeth but they pass through soft tissue and gaps such as cracks in bones. Low-energy X-rays do not carry enough energy to destroy cancerous tumours, so high energy X-rays must be used
