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physics > p13 - electromagnetic spectrum > Flashcards

p13 - electromagnetic spectrum Flashcards

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1
Q

electromagnetic waves and their properties

A
  • a continuous spectrum of waves
  • transverse waves
  • they can travel at the same speed in the same material (speed of light 3 x 10^8)
  • can travel through a vacuum because they’re vibrations of electric and magnetic fields, not particles
  • obeys the wave equation
  • they are produced naturally by stars and living things but also by man-made objects like appliances
  • cannot be detected by the human eye
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2
Q

what increases/decreases in the electromagnetic spectrum?

A
  • wavelength decreases
  • energy and frequency increases
  • the penetrating ability increases
  • increased risk to humans (as the energy increases)
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3
Q

how do you calculate the speed of an EM wave?

A
  • use the wave equation
    it should always be the speed of light (3 x 10^8) remains constant
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4
Q

radiowaves and their properties

A
  • they have the longest wavelength (from a few cm to several km)
  • have the lowest energy

penetration:
- can easily pass through air
- can pass through solids, can also diffract around objects of a similar size or smaller to their wavelength
- cannot go through the ionosphere (it reflects them instead)

uses: transmitting radio and television programmes

there are no known hazards

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5
Q

microwaves and their properties

A
  • wavelengths of around 0.1cm to 10cm

penetration:
- can pass easily through air and the earth’s atmosphere
- good for transmitting information from one place or another because microwave energy can penetrate clouds, light etc.

uses:
- cooking food; microwaves are absorbed by the water molecules in the food. the energy

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6
Q

what happens when waves meet materials

A
  • transmitted: wave carries in travelling but the speed and direction changes - refraction
  • absorbed: energy transferred to the material and can cause 1) an increase in the thermal store of the material and 2) electrons in the wires of a receiver to oscillate, creating a current
    => what happens depends on the type of wave
  • energy increases along the EM spectrum and the higher the energy, the more able it is to penetrate materials
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7
Q

microwaves

A
  • are low energy and long wavelengths
  • used for satellite communication, mobile phones and cooking food in microwaves
  • they are suitable for these uses because they penetrate the ionosphere to reach satellites and can penetrate the surface of food to cause heating
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8
Q

infrared

A
  • a type of electromagnetic wave
  • higher in energy than microwaves and radiowaves
  • shorter wavelengths than radiowaves and microwaves
  • it is felt as heat - all objects absorb and emit infrared radiation
  • used for electric heaters, security systems, thermal imaging and night vision - the hotter an object is, the more infrared radiation/thermal radiation it is emitting
  • the infrared radiation emitted by all objects can be detected using cameras to form a thermal image. hotter images emit more IR radiation
  • heaters transmit energy to the environment to be absorbed by people and air
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8
Q

visible

A
  • medium energy and wavelength waves
  • used for fibre optic communication
  • suitable for this use because visible light reflects its way along the internalsurface of the fibre to reach from one end of an optical fibre to the other with no loss. It allows fast data transmission.
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9
Q

ultraviolet (UV)

A
  • higher energy than visible light.
  • shorter wavelength than visible light.
  • used for checking for fraudulent bank notes, sterilising medical equipment, sun tanning, energy efficient lamps
  • suitable for sun tanning because UV can penetrate the skin, causing pigmentation to increase. (over exposure to UV is dangerous!)
  • suitable for energy efficient lamps and checking bank notes because UV is absorbed by some materials and then the energy re-emitted as visible light
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10
Q

x-rays

A
  • high energy and short wavelength waves.
  • used for diagnosing broken bones, sterilising fruit and medical equipment, cancer treatment
  • suitable for diagnosing broken bones because they can penetrate soft tissue, but not bone (absorbed by the bone), so this means breaks in a bone can be visualised.
  • suitable for cancer treatment because high doses can penetrate through flesh to kill living cells
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11
Q

gamma

A
  • very high energy and very short wavelength waves
  • used for sterilising fruit, medical tracers & cancer treatment
  • suitable for these uses because gamma rays can penetrate pretty much anything to kill cells. – also when a gamma emitting source in inside the body, the gamma rays can pass out from the body and be detected (gamma knife)
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12
Q

effect of surface colour on infrared radiation

A
  • apparatus: two beakers (one matt and one shiny), thermometer, hot water
  • fill both with the same temperatures of hot water
  • check and record the initial temp
  • after 10 minutes there should be an obvious drop in temperature which should be shown from the table
  • record the final temperatures
  • calculate temperature change
  • independent: colour of the surface of the beaker
  • dependent: change in temperature/ temperature drop
  • control: initial temperature, volume of water
  • making results reproducible: check the pattern in your results is the same/similar to the experiments that have been carried out with the same method
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13
Q

which surface is the best absorber and emitter?

A

matt, black surfaces

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14
Q

which surface is the worst absorber and emitter? and why?

A

shiny, white surfaces because they reflect most of the radiation away

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15
Q

effect of surface colour on infrared radiation: leslie cube

A
  • apparatus: leslie cube, digital thermometer, hot water
  • fill up a leslie cube with hot water (on a heat proof mat)
  • measure the initial infrared radiation using a digital thermometer - hold 10 cm away
  • wait 10 minutes and then measure the final infrared radiation- calculate the change in emission
  • repeat for each surface of the cube
  • make sure that the thermometer is the same distance away from the cube: control
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16
Q

real life examples of infrared radiation

A
  • solar panels - the outside is dull and black as this will ensure that maximum heat absorbed
  • summer sports uniform - often white to reflect heat and help the players stay cool
  • foil to keep something warm - cold sandwiches wrapped in shiny aluminium foil to stay cool. hot sandwiches stay warm because there is no heat being emitted
  • thermal blanket - used to keep a marathon runner warm as it has a light, shiny surface to reflect his body heat back to him
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17
Q

EM waves in order

A

radio, microwaves, infrared, visible, ultraviolet, x-rays, gamma rays

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18
Q

what could happen when an EM wave meets a surface?

A
  • reflected off the material
  • transmitted or refracted through the material - depends on the angle
  • absorbed into the material
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19
Q

which factors affect a wave’s ability to penetrate?

A
  • depends on the type of wave and the type of material
  • the higher the energy of the EM wave, the more able it is to penetrate
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20
Q

which EM wave is the most penetrating and why?

A

gamma rays as they transfer the most energy

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21
Q

waves used for communication

A
  • radio
  • microwave
  • infrared
  • visible
22
Q

cancer-causing waves and why?

A
  • UV - skin
  • x-ray -
  • gamma rays - anywhere in the body
    high frequency waves > lots of energy > lots of damage
23
Q

harmful radiation

A
  • some waves can have harmful effects on human tissues, which depends on the dose and type of wave
24
Q

what is radiation measured in?

A
  • measured in sieverts (Sv)
  • 1000 millisieverts = 1Sv
25
Q

how is UV damaging? and what are the effects?

A

UV radiation damages surface cells which can lead to:
- sunburn
- premature aging of skin
- blindness
- increased risk of skin cancer

26
Q

how does a microwave oven work?

A
  • microwave ovens can be used to cook food quickly
  • microwaves are absorbed by water molecules in the food, and these molecules vibrate more, increasing their kinetic energy - heating the food because KE is directly proportional to temperature
27
Q

what are the dangers of microwaves?

A
  • microwaves can penetrate the body: they cause water molecules in the body to vibrate more, raising the body’s temperature and heating the person from the inside
28
Q

how are microwaves used in communications?

A

shorter wavelengths carry more information and spread out less, but have a shorter range because of the increasing absorption by the atmosphere

29
Q

which two types of waves do communications use?

A
  • radiowaves
  • microwaves
30
Q

what are the different ranges of microwaves and radio waves? and what are their functions?

A
  • microwaves and near microwaves: spread out less than radiowaves so the signal doesn’t weaken as much ~ mobile phones, satellite phones and satellite TV
  • radio waves < 1m: carry more information than longer wavelength radio waves ~ TV broadcasts
  • radio waves 1m-100m: range is limited to the area around the transmitter ~ local radio stations, emergency services
  • radio waves > 100m: longest range ~ national and international radio stations
31
Q

what are carrier waves and what do they do?

A
  • when sound waves reach a microwave they INDUCE an alternating current called an audio signal
  • an oscillator provides a carrier wave in the form of an alternating current
  • the transmitter uses the carrier waves in the form of an alternating current
  • the transmitter uses the audio signal to modulate the carrier wave (changing its amplitude and/or frequency) [UNIFINISHED CARD]
32
Q

why do we need carrier waves?

A

so that the frequency of the oscillations in the circuit is high enough for radiowaves to be emitted

33
Q

what are optical fibres and how do they work?

A
  • visible light and infrared waves can be used to transmit information down a hollow transparent glass fibre.
  • the waves are reflected along the fibre, rather than transmitted to the air outside - TOTAL INTERNAL REFLECTION (no refraction at all)
34
Q

why are shorter wavelengths better to carry information?

A
  • visible light and infrared have shorter wavelengths than radio waves so more information can be carried in the pulse of waves
  • this allows the signal to stay in the fibre
  • this is beneficial because the information sent along the fibre is more secure compared to a radiowave which can be intercepted by any receiver
35
Q

how are radio waves different to sound waves?

A
  • radiowaves can travel through a vacuum
  • radiowaves can travel at the speed of light
  • radiowaves are transverse, soundwaves are longitudinal
36
Q

what are some uses of infrared radiation?

A
  • electrical heaters
  • cooking food
  • thermal cameras
37
Q

which part of the electromagnetic spectrum transfers the least energy per second

A

radio waves

38
Q

what is energy per second?

A

rate

39
Q

what is a danger of visible light?

A

light that is too intense can cause damage to the retinas in your eyes and cause blindness

40
Q

how/where are x-rays produced?

A
  • produced in an x-ray tube
  • heated filament emits electron by thermionic emission
41
Q

how/where are gamma rays produced?

A
  • produced by nuclear decay
  • it is just energy, no mass
42
Q

what are the dangers of UV radiation? and how can they be overcome?

A
  • can damage skin cells, leading to skin cancer. it can burn the skin and eyes + premature aging
  • this can be mitigated with clothing, glasses or sun cream, which blocks the UV radiation from reaching the skin or eyes
43
Q

what are the dangers of x-rays and gamma rays?

A
  • these forms of radiation are ionising
  • low doses ionising radiation can ionise the atoms in our genes, mutating them and increasing the risk of cancerous tumours.
  • high doses of ionisng radiation can kill cells immediately, leading to something called radiation sickness
44
Q

what does being ionising mean?

A
  • electrons in an atom’s energy levels can absorb the energy transferred by em radiation and escape their atom, forming a free electron and a positive ion
  • the electron can then escape the cell and harm our genes
45
Q

how can a radiation dose be measured?

A
  • by wearing film badges that detect over-exposure
  • it is measured in sieverts and represents the risk of harm resulting from exposure to radiation
  • it depends on the amount of time exposed to radiation and how much energy is transferred by the radiation
46
Q

what are some uses of UV?

A
  • can be used in lamps, as invisible security tags, anti-forgery designs in banknotes, and in sun-tanning
47
Q

what can x-rays be used for?

A
  • can be used to detect cracks in objects
  • denser media absorbs x-rays more
48
Q

what can gamma rays be used for?

A
  • can be used to kill bacteria - sterilising food or surgical instruments
49
Q

what can happen when a wave meets a new medium?

A
  • transmits
  • reflects
  • refracts
  • absorbs
50
Q

how do x-rays work?

A
  • x-rays are produced in an x-ray tube, which then pass through patient’s body
  • the waves are absorbed by dense materials like bone, metal, teeth or a contrast medium that fills soft yissue and absorbs x-rays more than the surrounding tissue, showing the inside of the tissue (eg. a barium meal)
  • a flat-screen detector below the patient contains a charge-coupled device. the CCD’s sensors detect x-rays and convert it to visible light, which then creates electronic signals in the sensors that can be processed by a computer to create a digital image
  • lead plates can be used to shield parts of the patients’ body
51
Q

what is a PET scan used for?

A
  • figures out what is wrong with a specific part of the body; find the location of a tumour
52
Q

what can x-rays and gamma rays be used to treat?

A

cancerous tumours

53
Q

why is the source of gamma rays or x-rays always rotating?

A
  • because if too much ionisng radiation is directed at one part of the body then it will start to kill healthy cells, as well as cancerous cells
    if it’s rotating, it will always hit the cancerous cells but will only hit the healthy cells at a low dosage and not killing them
  • surrounding tissue can also be shielded with lead plates

physics (5 decks)

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