P2

EM radiation Movement of energy in the form of a wave Movement of energy NOT matter Energy moves in packets called photons High frequency EM waves carry more energy per photon than lower frequency waves Radio waves – longest wavelength, lowest frequency Gamma – shortest wavelength, highest frequency Order – radio, micro, i-r, visible, UV, X-ray, gamma All travel at 300,000 km/s in a vacuum

Effect and intensity When an EM wave hits an object it can do one of the following: Pass through material (x-ray in tissue) Be absorbed by the material ( x-ray in bone) Reflect off material (visible light on a mirror) Can heat up material (cooking food in microwave) The material that emits the radiation is the source The “intensity” of an EM wave is the strength of the energy reaching a square metre each second Depends on the number of photons reaching that material per second And the amount of energy in each photon Intensity is affected by distance.....the further away an object is the more energy will be absorbed by the surroundings and not reach the object This is because the surface area the wave covers as it travels to the object will increase

Ionisation/heating High energy waves cause ionisation This involves removing electrons from molecules/atoms, turning them into ions This can be damaging to cells as ionisation can cause mutations to occur in the chemical structure of DNA This can kill the cell or cause a tumour to form, resulting in cancer UV, x-ray and gamma rays Concerns with effect of microwave radiation Microwaves heat water molecules (microwave works) How are we protected from radiation from microwaves? Metal casing and door protector reflects microwave radiation back into appliance (absorb some) Fears that microwaves emitted from mobile phones/masts could cause heating of water molecules within cells with enough exposure Could cause damage to cells and tumours to develop No evidence from studies to confirm this

UV/x-ray Some materials emit ionising radiation all the time e.g. Radioactive elements, sun Some elements emit gamma radiation all the time (Uranium) and so are very dangerous – high intensity exposure to ionising radiation can cause radiation sickness Some people (radiographers) are exposed to radiation on a regular basis. Wearing lead lined aprons absorbs high energy radiation and protects them from cancer risks X-rays are used to view bones and objects in airport luggage. These materials absorb the x radiation and can then be seen on an x-ray image The sun emits UV radiation Ozone (O 3 ) is a layer of gas in the Earth’s atmosphere What is the importance of the ozone layer for UV protection? Absorbs a lot of the sun’s UV radiation, protecting us from its harmful effects UV causes ozone to form UV splits an O 2 molecule into 2 atoms, each of these combines with another O 2 molecule to form O 3 How can we protect ourselves from UV over exposure? Wearing clothes, sunscreen, not going outside during peak sunlight hours (12 pm – 2.00 pm)

Greenhouse effect Sun emits high energy radiation and the Earth absorbs some of this – heats the Earth But....some EM radiation is then emitted back out into space, prevents us from getting too hot Most of the EM radiation emitted back out from the Earth is as i-r so has a lower frequency than the radiation emitted by the sun This is because the Earth is cooler A lot of this i-r radiation is absorbed by greenhouse gases in the atmosphere These gases are carbon dioxide, methane, water vapour The gases re-radiate the EM radiation in all directions, including back onto the Earth This trapping of heat on the Earth is called the “Greenhouse effect” Without this “greenhouse” effect, the Earth would be too cold for us to live on

Carbon cycle

Photosynthesis – removes carbon dioxide from the atmosphere to make carbon compounds in the plant Respiration – returns carbon dioxide to the atmosphere from plants/animals/decay organisms respiring and making energy These two processes keep the level of carbon dioxide in the atmosphere constant (0.035%)

Global warming Population is rising – using more fuels for energy (burning more fossil fuels for cars, electricity etc.) Releasing more CO 2 into the atmosphere Increased population – increased respiration from people and cattle Deforestation – removing trees to build new homes and grow food – removes plants that photosynthesise So less CO 2 being removed from the atmosphere Increased levels of CO2 means that more heat is trapped in the atmosphere, rather than being released into space So the Earth’s global temperature is rising This is resulting in climate change, a big shift in normal weather patterns, causing droughts in some parts of the world and floods in others