Presentation on theme: "The Electromagnetic Spectrum"— Presentation transcript:
1The Electromagnetic Spectrum WAVES IN ACTIONTheElectromagneticSpectrum
2What Is The Electromagnetic Spectrum? We are all familiar with LIGHTLight is part of the EM spectrum – it is an electromagnetic wave.There are several different types of EM waves.The EM spectrum is a way of classifying all the types of waves according to wavelength
3What are Electromagnetic Waves? Electromagnetic waves are just like any other wave, with one exception:They are the only type of wave that can travel through a vacuumThey are transverse wavesThey all travel at the same speed: 300,000,000 m/s (3x108 m/s)
6Radio WavesCreated by oscillations (vibrations) of electrons in a conductor.Very long wavelength (few km to few cm) – low frequency – so low energy waves.Used to transmit radio and TV signals.Travel in straight lines, but can be bounced off the upper atmosphere, so can travel around the world.
8MICROWAVES Wavelength from cm to .0001 m Used for cooking food Microwaves make water molecules vibrate, which causes food to get very hot very quickly.Penetrate only a few cm, the heat is then carried inside by conduction
9MICROWAVES Microwaves are also used for communication. Mobile telephones use microwaves.They are also used to communicate with satellites as they can pass through the upper atmosphereThey also do not spread out much, so they are easy to use with a dish.
11INFRA-RED Wavelength from mm to 0.000001m. Most familiar use is for cooking and heating, like electric grills and heaters.Infra red waves are easily absorbed at the surface of things, making them hot, then heat is carried inside by conduction.
12INFRA-RED Everything gives out Infra-red This allows cameras to use IR instead of visible light for night-vision.They are also used for thermo-imaging cameras, to find people buried in earthquakes. They will be being used in New York.They are also used for remote controls
17ULTRA VIOLETShorter wavelength – m to m, frequency higher.Carry more energy, and can penetrate top layers of skin, damaging the lower layersThis can cause sun burn, and possibly skin cancer of a long period of time.The eyes are very sensitive to UV, so sunglasses should always be worn in bright sunshine.Most UV radiation from the sun is filtered by the ozone layer.
18Ultra VioletUV can be used to sterilise things, as bacteria can be killed by UV.UV is also used for anti-counterfeit purposes in bank notes.UV tubes are used in entertainment venues – they make white clothes glow
20X-RAYS Discovered accidentally by Wilheim Röntgen in 1895 Very short wavelength ( m to m) – so a very high frequency.Very energetic – can pass through your body.Produced by firing electrons at a metal target
21X-RaysTheir ability to pass through soft tissue, but not bone, makes them very useful in medicine.They are completely stopped by metals, making them useful for security scanning at airports.
22X-RaysBecause they carry a lot of energy they can easily damage or kill cells.This can lead to cancer if over-exposure occurs.Very small amounts are used in hospitals and are relatively safe, however the operator will stand behind a lead screen to stop unnecessary exposureX-rays are also used to treat cancer by killing cancerous cells.
24GAMMA RAYSExtremely short wavelength ( to m)Extremely high frequency, so carry a large amount of energy.Gamma rays arise from the nuclei of unstable atoms.
25GAMMA RAYSVery harmful to living things – they can easily kill or damage cells leading to cancer.They are used to sterilise hospital equipment as bacteria are killed instantly on exposureThey can also be used to kill bacteria in food. This is known as irradiation.
26GAMMA RAYSA very important application of gamma rays is the treatment of cancer.More effective than X-rays because they carry more energy.Careful focussing of gamma rays avoids damage to healthy cells.
27Tracers Particles which give out gamma rays can be used for “tracers”. A small amount of radioactive material is injected into the patientThe movement of radiation can be monitored from outside the body.This allows doctors to pick up problems, such as poor blood circulation, as well as detecting tumours.
28RISKS and BENEFITS X-Rays and Gamma rays are both used in medicine. Their benefits are they destroy cancer, and avoid surgery, as well as use for diagnostic purposes.They can also cause cancer, and may cause sickness if exposures are too large.
29ELECTROMAGNETIC SPECTRUM THE COMPLETEELECTROMAGNETIC SPECTRUMLongWAVELENGTHShortGammaRaysInfraRedUltraVioletRadioMicro-WavesVisibleX-RaysLowFREQUENCYHighLowENERGYHigh
30IMPORTANT NOTES All EM waves travel at the same speed Different parts of the EM spectrum have different propertiesThe higher the frequency of EM radiation, the higher the energy it carries.