waves in action the electromagnetic spectrum what is the electromagnetic spectrum? we are all...
Post on 26-Mar-2015
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Slide 2 WAVES IN ACTION The Electromagnetic Spectrum Slide 3 What Is The Electromagnetic Spectrum? We are all familiar with LIGHT Light 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 Slide 4 What 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 vacuum They are transverse waves They all travel at the same speed: 300,000,000 m/s (3x10 8 m/s) Slide 5 Slide 6 The Electromagnetic Spectrum Slide 7 Radio Waves Created 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. Slide 8 The Electromagnetic Spectrum Slide 9 MICROWAVES 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 Slide 10 MICROWAVES 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 atmosphere They also do not spread out much, so they are easy to use with a dish. Slide 11 The Electromagnetic Spectrum Slide 12 INFRA-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. Slide 13 INFRA-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 Slide 14 The Electromagnetic Spectrum Slide 15 VISIBLE LIGHT This is the EM wave we are most familiar with. Different colours have different wavelengths, from red (longest) to violet (shortest). Slide 16 THE VISIBLE SPECTRUM RED ORANGE YELLOW GREEN BLUE INDIGO VIOLET The full spectrum is: These can be remembered using: Richard Of York Gave Battle In Vain ! Slide 17 The Electromagnetic Spectrum Slide 18 ULTRA VIOLET Shorter wavelength 0.000001m to 0.000000001m, frequency higher. Carry more energy, and can penetrate top layers of skin, damaging the lower layers This 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. Slide 19 Ultra Violet UV 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 Slide 20 The Electromagnetic Spectrum Slide 21 X-RAYS Discovered accidentally by Wilheim Rntgen in 1895 Very short wavelength (0.00000001m to 0.000000000001m) so a very high frequency. Very energetic can pass through your body. Produced by firing electrons at a metal target Slide 22 X-Rays Their 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. Slide 23 X-Rays Because 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 exposure X-rays are also used to treat cancer by killing cancerous cells. Slide 24 The Electromagnetic Spectrum Slide 25 GAMMA RAYS Extremely short wavelength (0.0000000001 to 0.000000000000001 m) Extremely high frequency, so carry a large amount of energy. Gamma rays arise from the nuclei of unstable atoms. Slide 26 GAMMA RAYS Very 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 exposure They can also be used to kill bacteria in food. This is known as irradiation. Slide 27 GAMMA RAYS A 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. Slide 28 Tracers Particles which give out gamma rays can be used for tracers. A small amount of radioactive material is injected into the patient The 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. Slide 29 RISKS 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. Slide 30 THE COMPLETE ELECTROMAGNETIC SPECTRUM LongShortWAVELENGTH FREQUENCYLowHigh ENERGY LowHigh Slide 31 IMPORTANT NOTES I.All EM waves travel at the same speed II.Different parts of the EM spectrum have different properties III.The higher the frequency of EM radiation, the higher the energy it carries.