Flashcards
Physics P2
Flashcards do conjunto (24)
- 1P2.1 ELECTROMAGNETIC RADIATION . Light is a type of EM radiation . Radiation is just a transfer of energy .Visible light is radiation that our eyes can detect . There are 7 types of radiation altogether, making up the ELECTROMAGNETIC RADIATIONELECTROMAGNETIC SPECTRUM
Radio waves
Micro waves
Infra red
Visible light
Ultra violet
X-Rays
Gamma rays - 2EM RADIATION CONTINUED . All types of EM radiation is a transfer of energy . The energy is delivered as photons - a photon is a ting droplet or packet of energyENERGY TRANSFER AMOUNT
. Each photon carries a ting amount of energy
. But not all photons have the same amount of energy
- the amount of energy depends on the frequency of the radiation
. The FREQUENCY, and so photon energy, INCREASE as you go along the electromagnetic spectrum
. Radio wave photons have the lowest frequency and energy
. Gamma ray photons have the highest frequency and energy - 3EM RADIATION AND HOW IT IS EMITTED . Objects emit radiation - This is called a SOURCE . Once radiation has been emitted it spreads out until it reaches some matter . 3 things can happenThe radiation can be
. Transmitted - just keep going, like light passing through glass
. Reflected - bounce back, like reflected from a mirror
. Absorbed - like a sun bather absorbing UV rays from the sun - 4. What happens depends on the substance is like and the type of radiation . 2 or 3 of these things can happen at the same time . Radiation can be absorbed by objects a long way from the source . Objects that absorb the radiation are called DETECTORS - our eyes are light detectors. All types of radiation can travel through space (a vacuum)
. In the vacuum all radiation travels as the same speed
. The SPEED OF LIGHT
.300,000 km/s - 5INTENSITY . When radiation is absorbed by matter, the photons transfer their energy to the matter . Energy deposited by the beam of photons depends on: - how many photons there are -the energy of each photon. INTENSITY - how much energy arrives at each square metre of surface area per second
- unit = W/m^2 (watts per square metre)
. The intensity of the beam of radiation decreases with the distance from the source
because:
- the beam spreads out
- the beam gets partially absorbed as it travels - 6IONISATION . All substances are made of atoms and molecules . When a photon hits an atom or molecule, it sometimes has enough energy to remove an electron and change the atom or molecule .THIS IS CALLED IONISATION . Some radioactive materials emit ionising gamma radiation all the time. The change of an atom or molecule can initiate other chemical reactions
. It takes a lot of energy to remove an electron from a atom or molecule
. only radiation with a high enough amount of photon energy can cause ionisation
( ultraviolet, x-rays and gamma rays) - 7P2.2 DANGER OF IONISATION . The heating effect of absorbed radiation can damage living cells . If body cells are exposed to ionising radiation, the damage to DNA molecules can cause mutations - it may then start dividing over and over again without stopping - this is cancer. Very high doses of radiation can kill you cells altogether - this is what happens in radiation sickness
. UV radiation is ionising and can damage living cells in the skin
- leads to sunburn and then possibly skin cancer
. Increased exposure causes more damage - 8PROTECTION AGAINST DANGEROUS RADIATION . UV RADIATION - clothes, sun cream . X-RAY - lead shield over parts of the body that aren't being examined - the lead absorbs the rays . radiographers wear lead aprons or stand behind concrete to protect themselvesHEATING
. Non-ionising radiation doesn't have enough energy to change atoms
. When absorbed it transfers energy to the atom or molecule of the substance
- this transfer of energy causes heating
.More intense radiation + longer exposure time = greater heating effect
. Heating effect can damage living cells - 9MICROWAVES . Make particles vibrate - heating them up . Waves are strongly absorbed by water molecules - so can heat up things containing water .Microwaves often come in different power ratings - higher power = higher intensity radiation - less time needed to produce the same heating effect - food cooks more quickly. Microwave radiation would heat up the water in your body's cells if you were exposed to it
. MW ovens have metal cases and screens over their glass doors which reflect and absorb the microwaves stopping them getting out - 10HEALTH RISKS WITH MICROWAVES . Mobile phones - emit radiation when a call is being made . Some of this radiation is absorbed by your body - causes heating to your body tissues . Concerns over heating of brain and jaw tissues causing medical conditions - including cancer - no conclusive evidence to show this though. The radiation is quit low intensity
- heating is very minor and nothing to be worried about
. PHONE MASTS - emit the radiation
- people that live very close worry about it
- isn't much evidence
- any health problems may take a long time to emerge - 11EM RADIATION AND THE ATMOSPHERE . Gasses in the atmosphere filter out certain types of radiation from the sun - absorb or reflect the radiation . Some types of radiation pass through quite easilyPROTECTION BY OZONE LAYER
. Protects us from too much UV radiation
. Ozone is a form of oxygen
- ozone molecule is just a three oxygen atoms joined together
. It occurs naturally at a certain hight in the atmosphere
. When an ozone molecule O3, absorbs UV radiation, it splits it into O2 AND O
- so the reaction is reversible
- causing a chemical change each time - 12P2.3 GREENHOUSE EFFECT . All objects emit EM radiation with a principal frequency that increases with temperature . Earth allows some EM radiation to pass through it from the sun . The radiation that does get through warms the earth's surface. Most radiation emitted from the earth is infrared radiation - heat
. It is a lower principle frequency than what is emitted from the sun because the earth is much cooler
. A lot of the infrared radiation is absorbed by atmospheric gases
- carbon dioxide , methane, water wapour - 13. The gases then reflect / re-radiate heat in all directions including back to earth . So the atmosphere acts as a insulating layer - stopping the earth from loosing at its heat at night . This is all known as the GREENHOUSE EFFECTXXXXXXXXXXXXXXXXXXXXXXXXXX
- 14THE CARBON CYCLE
- 15. All the carbon on earth moves in one big cycle . Processes that return CO2 back into the atmosphere: - Respiration in plants and animals -Respiration in decomposers .all plants and animals contain carbon, when they die, decomposers (bacteria and fungi) break them down .as they do, they respire and produce CO2 -Burning ( trees and coal)..Photosynthesis in green plants and other organisms removes carbon dioxide
. For thousands of years these processes all balanced out
.So the concentration og CO2 in the atmosphere has been almost constant - 16HUMAN ACTIVITY IS UPSETTING THE CARBON CYCLE . Amount of carbon dioxide in the atmosphere has slowly been increasing over the last 200 years - CO2 is being released into the atmosphere quicker than it being removed.This is mainly because peoples lifestyles have changed
1.Using more electrical gadgets, cars and planes
- more energy then need sot be made
- its mainly made from fossil fuels
-which release more carbon dioxide - 172. The population is rising . More land is needed for building houses and growing food - space is made by chopping down and burning trees - this increases the amount of CO2 that is released. Plants are the main thing that remove carbon dioxide
- fewer trees = less carbon dioxide removed
- burning trees adds a lot of CO2 into the atmosphere - 18GLOBAL WARMING . Global temperature rise . Evidence shows that rise in carbon dioxide is causing global warming . There is now a SCIENTIFIC CONSENSUS that humans are causing global warming - Computer climate models provide this evidenceCOMPUTER MODELS
. It is a great big load of equations linking various parts of the climate system
- try to mimic what goes on in the real climate by doing calculations
.Once computer is programmed, data has to be entered
-temp. of surface of ocean in different areas
- then tell you what is going to happen - 19. Also used to explain why the climate is changing now - earth climate varies naturally - eg. changes in orbit cause ice ages . Climate modelling shown that over the last few years natural change don't explain the current global warming - so the increase is due to human activityCONSEQUENCES OF GLOBAL WARMING
1. Sea getting warmer - so expanding = sea levels rising
. sea level has risen a little bit over the last 100 years
- bad for people living in low lying area (netherlands,east anglia and maldives) - 202. High temperature cause ice to melt - runs off land and causes sea levels to rise 3. GW causes changes in weather patterns - suffer from more extreme weather .longer hotter droughts, hurricanes - Extra heat also increases stronger winds = more rain = more storms and floods - Effect food production . some regions are now too dry to grow foods and some are too wet . this will get worse as temperature increasesEM WAVES AND COMMUNICATION
TRANSMITTING INFORMATION
. EM radiation has been used to send information for years
. Different frequencies are used for different things
- INFRARED - tv remotes, night vision cameras
- MICROWAVES - mobile phones, satellite communication
- RADIO - tv and radio transmittions, radar - 21RADIO WAVES . Good at transmitting over long distances - it doesn't get absorbed by the earth atmosphere as much as most waves . Waves that are used to transmit tv and radio have very short wave lengths compared to most radio wavesMICROWAVES
. Used for communication to and from satellites ( tv and phones)
- microwaves can pass through the atmosphere easily
. For satellite tv:
- signal from transmitter is transmitted into space
- absorbed by the satellite receiver dish orbiting thousands of km above earth
- satellite transmits the signal back to earth in a different direction
- received by satellite dish on the ground
. dishes are made out of metal - metal reflects microwaves - dish focuses the waves into the receiver - 22INFRARED AND LIGHT . Optical fibres work by bouncing waves off the insides of a thin inner core of glass or plastic . Wave enters one end of the fibre and is reflected repeatedly until it emerges at the other end . light and infrared are good for transmitting along optical fibres - the signal doesn't weaken much as it travels along - glass doesn't absorb much of the radiationANALOGUE AND DIGITAL SIGNALS
. Information is being transmitted everywhere all of the time
1. whatever you are sending (text, sound, photo) it is all converted into electrical signals before it is transmitted
2. It is then send long signals down telephone lines
OR
3. SUPERIMPOSED (mixed) into carrier EM waves
4. then sent out as either analogue or digital - 23ANALOGUE SIGNAL . The amplitude or frequency of an analogue signal varies continuously . Can take ANY value in a particular rangeDIGITAL SIGNAL
. Can only take one of a small number of discrete values
-eg. on or off , true or false
. Information is carried by switching the EM carrier wave on and off
. This creates pulses - short bursts of waves
- eg. 0=off 1=on
- A digital receiver will decode these pulses to get a copy of the original signal - 24AMPLIFYING SIGNALS . Both signals weaken as they travel so need to be amplified along their route . Interference and noise from electrical disturbances or other signals can be picked up along the wayDIGITAL IS FAR BETTER QUALITY
. Noise is less of a problem with digital
- it is still obvious what the signal is meant to be
. If a noisy analogue is received it is difficult to know what the original signal was meant to be
. So digital is a lot better quality
. Also can transmit several signals at once using just one cable or EM wave with digital signals
. Digital is easier to process using a computer
- computers are digital devices
. Amount of info used to store a digital image or sound is measured in bytes
- image and sound will be of higher quality when the amount of info stored is higher
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- gcse physics FlashCards sobre Physics P2, criado por heather jenkinson em 17-04-2016.
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- heather jenkinson
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