- Light is a type of electromagnetic radiation.
- Radiation is the transfer of energy, it is transfered through photons.
- They're are seven types of radiation making up the electromagnetic spectrum; Radio waves, Microwaves, Infrared, Visible light, Ultraviolet, X-rays, and Gamma rays.
- The amount of energy carried by a photon depends on the frequency of the radiation.
- Radio wave photons have the lowest frequency and the least energy.
- Gamma ray photons have the highest frequency and the most energy.
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Electromagnetic radiation and energy
- Any object that emits radiation is called a source.
- In a vacuum (space) all electromagnetic radiation travels at the same speed, this is the speed of light.
- Radiation can be transmitted (just keep going), reflected (bounce back), or absorbed.
- Two of these things can happen at the same time.
- Intensity decrease as the distance from the source increases.
- Total energy= number of photons X energy of each photons
- The intensity if measured in W/m^2 (watts per square metre)
- The intesity of a beam of radiation decreases with distance from the source because; the beam spreads out, and it gets partially absorbed as it travels.
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- All substances are made of atoms and molecules. When a photon hits an atom it sometimes has enough energy to remove an electron and change the atom. This is ionisation.
- These atoms can start other chemical reactions.
- Only ultraviolet, X-rays, and gamma rays have enough energy to do this. They are ionising radition.
- If your cells are exposed to ionising radiation they damage the DNA molecules and cause mutations. This might mean the cells begin to divide over and over again without stopping. This is cancer.
- We're all exposed to ultraviolet radiation from the sun. This can lead to sunburn or even skin cancer.
- You need protection against dangerous radiation.
- Lead absorbs X-rays. They pass easily through flesh but are absorbed by denser materials like bone.
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Uses of electromagnetic radiation
- Non-ionising radiation (light) doesn't have enough energy to change atoms.
- It can however cause heating. The more intense the radiation and the longer the exposure, the greater heating effect.
- Microwaves make particles vibrate, heating them up.
- Microwaves are used to send signals between mobile phones and mobile phone masts.
- Some of the radiation from your phone could be absorbed by your body, causing heating. Some people are concerned that the heating of the brain and jaw could cause cancer, however there isn't any conclusive energy for this though.
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Electromagnetic radiation and the atomsphere
- Some radiation from the sun passes through the atomsphere, mainly visible light and radio waves.
- The greenhouse effect helps regulate Earth's temperature.
- Energy from the sun is absorbed by the Earth. The Earth radiates heat which is absorbed by greenhouse gases, and re-radiated in all directions.
- The ozone layer protects us from too much UV radiation, as it absorbs the radiation.
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Humans and the carbon cycle
- Over the last 200 years the concentration of carbon dioxide has been inreasing.
- This is because people's lifestyles have changed. We travel more in cars and planes. We get these from fossil fuels that when burnt, produces carbon dioxide.
- The population is also rising so more land is needed for houses and crops. This space is often made by chopping down and burning trees. This adds to the levels of carbon dioxide as plants usually remove the carbon dioxide.
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Waves and communication
- Electromagnetic radiation can transmit infomation.
- Infrared; TV remote controls and night vision. Microwave; Mobile phones and satellite communication. Radio; TV and radio transmissions and radar.
- Radio waves and microwaves are good at transmitting infomation over long distance, this is because the don't get absorbed by the Earth's atomsphere as much.
- Radio waves used for Tv have very short wavelengths.
- Microwaves used for mobile phones have very long wavelengths.
- Communication to and from satellites use microwaves that can easily pass through the atomsphere.
- Infrared and light are used in optical fibres. They work by bouncing off the sides of a thin inner core of glass or plastic.
- Light and infrared are great for transmitting infomation along optical fibres as they don't weaken as they travel.
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