EM Radiation and energy
Radio, micro infrared, visible, UV, X-ray, gamma
- transfer energy in packets- photons
- types of EM transfer more energy than others, amount depends on frequency of radiation
- Frequency increases as you go along spectrum
- emitted from sources
- frequency of thermal radiation from an object increases with temperature
- they are transmitted, reflected or absorbed- it depends on the substance and type of EM
- Detectors absorb radiation
- Intensity decreases as the distance from the source increases
- Radiation is absorbed by matter, energy is also transferred
- Total energy = no. of photons x energy of each photon
- Intensity= how much energy arrives at each square metre per second (W/M2)
- Beam spreads out and is partially absorbed as it travels
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- A photon hits an atom/molecule and has enough energy to remove an electron causing it to be positively charged
- the changed molecule/ atom can then go and initate other chemical reactions in the body
- it takes a lot of energy to remove an electron from an atom or a molecule, so the only types of EM that can cause ionisation are; UV, x-ray and gamma. These are all ionising radiation.
- It is dangerous if it happens in your cells because the damage to DNA molecules can cause mutations, cells may start dividing over and over without stopping- cancer.
- Very high doeses of radiation can kill your cells all together- radiation sickness
- We are all exposed to radiation from the sun, UV is ionising and can damage living cells in the skin- can lead to sunburn or skin cancer.
- Increased exposure= more damage
Protection from dangerous radiation:
- UV = you can protect yourself with clothes and sunscreen
- X-rays= radiaographer may put lead shields over parts of body to avoid unnecerssary exposure, radiographer may wear an apron/ stand behind concrete.
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Uses of EM radiation
- EM can cause heating
- Non-ionising radiation doesn't have enough energy to charge atoms but, when it's absorbed it transfers energy and heats the atoms
- more intense and longer= greater heating effect
- Heating can cause damage to living cells e.g burning
- Heating can be useful to heat up food, infrared is used in standard ovens and microwaves are used in microwaves
- M.W make particles vibrate, heating them up. Some M.W are strongly absorbed by water and can heat things containing water (food)
- M.W ovens come in different power ratings, more powerful ovens produce higher intensity, so less time is needed to produce the same heating effect.
- M.Ws have a protective metal cases and screens to stop themwarming up your body cells.
- Health risks: M.W are used to send signals between mobile phones, when you make a call it emits radiation, some is absorbed by your body and causes heating in body tissues. There are concerns that heating of tissues like the brain and jaw could increase risk of some medical conditions, including cancer- no evidence yet. Radiation is quite low intensity too.
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EM and the atmosphere
- Some radiation passes through the atmosphere.
- The atmosphere filters out certain types of radiation from the sun and some types pass through quite easily.
- The Greenhouse Effect- helps regulate the Earth's temperature- too much= global warming
- Earth absorbs EM radiation from sun, warms up surface, it then emits some back out- cooling us down.
- most radiation emitted from Earth is infrared- heat. It is at a lower frequency than most of the radiation emitted by the sun because the Earth is cooler.
- Lots of this I.R is absorbed by atmospheric gases- CO2, methane and water vapour
- These then re-radiate heat in all directions, including back towards Earth.
- Atmosphere acts as an insulating layer, stopping heat loss at night.
- Ozone layer- protects us from too much UV radiation- ozone naturally occurs at a certain height in the atmosphere- 'the ozone layer'.
- When an ozone molecules (O3) absorbs UV, it splits into O2 and O- reversible reaction, causing a chemcial change each time. Ozone is mostly constant, but loss can cause there to be holes in the ozone layer- without ozone, a lot more UV radiation would reach us- IONISING RADIATION!!!
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Returns carbon to atmosphere=
- respiration (plants, animals and in decomposers-all plants and animals contain carbon, decomposers break them down when they die, as they do they respire and produce CO2)
- burning - trees/ fossil fuels
Takes away from atmosphere=
- Photosynthesis in green plants and other organisms.
CONC. HAS BEEN ALMOST CONSTANT FOR THOUSANDS OF YEARS- BUT HUMANS ARE UPSETTING IT!!! :(
- LIFESTYLE- more electronics used, needs energy.. burning fossil fuels..
- RISING POPULATION- more land needed to build houses and grow food, often made by cutting down and burning trees
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Global Warming and Climate Change
- Link between increased level of CO2 and increase in global temperature
- evidence suggests a rise in CO2 level is causing global warming by increasing the greenhouse effect.
- There's a scientific consensus that humans are causing global warming- a type of climate change, causes other types- e.g. changing weather patterns
- Scientists use computer models to understand climate change
- lots of equations linking various parts, mimicking real climate
- Program big computer with equations, you need data to start off calculations, computer uses this to work out various things and then uses them to work out globa air temperatures.
- Climate models can be used to explain current change too.
- Consequences would be pretty serious; sea level rising, ice melt, changed weather patterns, more extreme weather, extra heat, food production will suffer.
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EM waves and communication
- EM can transmit info: infrared (TV remotes and 'night vision' cameras) Microwaves (mobile phones and satellite communications) Radio (TV and radio transmissions and radar)
- Radiowaves are mainly used for communications on Earth: radiowaves and microwaves are good at trasmitting over long distances because they don't get absorbed by Earth's atmosphere as much as most of the spectrum
- Radio waves used for TV and FM radio transmissions have v. short wavelengths compared to most radio waves.
- Microwaves are used for mobile phone communications and have v. long wavelengths compared to most microwaves.
- Microwaves are used for satellite communications because some can pass easilt through the atmosphere.
- For a satellite TV, signal is transmitted into space where it's absorbed by the dish and transmits it back to Earth in different directions. Dishes= metal so rrelfects M.W well
- Infrared and light are used in optical fibres- O.F work by bouncing waves off the sides of a thin inner core of glass or plastic, wave enters one end of the fibre and is reflected repeatedly until it emrges at the other end, I.F and light are good because signal doesn't weaken as it travels along.
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Analogue and Digital
- Info is converted into signals before being sent long distances or superimposed onto carrier EM waves, then send out as either analogue or digital.
- Analogue: amplitude and frequency varies continuously, signal can take any value in a particular range, more difficult ot clean
- Digital: can only take one of a small number of discrete values- on or off/ 0 or 1. Digital reciever will decode thesepulses to get a copy of the originial signal. Easier to clean, higher quality, scan send several signals at once using just one wave- so more info. Also, easy to process using computers. Digital sound/ image is measured in bytes, better qual when the amount of info stored is higher.
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