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© Boardworks Ltd 2003 KS4 Waves : Dispersion and Electromagnetic radiation
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© Boardworks Ltd 2003 After this presentation you will be able to: Define dispersion. Describe how different colours are refracted different amounts. List the order of radiations in the electromagnetic spectrum. Recall the uses and dangers of the radiations in the electromagnetic spectrum. Describe how radio waves are reflected and diffracted. Recall the effect of EM radiation on living tissue. Describe how X ray images are formed. Describe the effects of incident EM radiation on materials. Recall the different absorption of EM radiation by different coloured skin. Explain how microwaves can heat up foods containing water. Describe how infrared radiation can be used to form heat images.
© Boardworks Ltd 2003 Dispersion Experiment 1. Connect a ray box to a power source. 2. Place a prism on a piece of plain paper. 3. Draw around the prism. 4. Shine a ray of light at the prism. 5. Draw in rays of light to show your observations. The ray box will get very hot. Take care!!!!!
© Boardworks Ltd 2003 Explaining dispersion The white light ray is split into a spectrum of colours. This is known as DISPERSION. The different colours of light have different wavelengths. Different wavelengths are refracted different amounts. Red light is refracted least. Violet light is refracted the most. Which colour is refracted the most? How do you remember the order of the colours? Richard Of York Gave Battle In Vain
© Boardworks Ltd 2003 Dispersion Summary Red/violet Refracted more/less by glass Longer/shorter wavelength Red/violet Refracted more/less by glass Longer/shorter wavelength
© Boardworks Ltd 2003 The Electromagnetic Spectrum Light, a type of radiation, is part of the electromagnetic spectrum. The electromagnetic spectrum is made up of different types of radiation. The different types of radiation have different properties and behaviour. All electromagnetic waves can travel through space. All electromagnetic waves travel at the same speed in a vacuum [300,000,000 m/s]. TRUE/FALSE
© Boardworks Ltd 2003 Colour, wavelength and amplitude We can see the relationship between colour, wavelength and amplitude using this animation.
© Boardworks Ltd 2003 Electromagnetic Spectrum Although all e-m waves travel at the same speed, their wavelength [ ] and frequency [ƒ] can be different. The properties, dangers and uses of e-m waves depends on the wavelength [ ]. Waves that cook food. Waves that cause sun-tans.
© Boardworks Ltd 2003 Electromagnetic Spectrum Radio Micro Infra- Red Light Ultra- Violet X rays Gamma Wavelength ( ) increases Can you think of a phrase that would help you remember this order? Gate X Usually Lets In Most Radiation High frequency Short wavelength High energy Most penetrating High frequency Short wavelength High energy Most penetrating Low frequency Long wavelength Low energy Least penetrating Low frequency Long wavelength Low energy Least penetrating
© Boardworks Ltd 2003 Electromagnetic Spectrum
© Boardworks Ltd 2003 Uses and dangers of EM radiation Research the uses and dangers of the various radiations: RadiationUsesDangers Gamma X-rays Ultraviolet Light Infra red Microwaves Radio waves
© Boardworks Ltd 2003 EM Radiation: Uses: Dangers: Kills harmful bacteria in food, sterilising surgical equipment, killing cancer cells. High doses can kill cells. Lower doses can cause cells to become cancerous. Gamma
© Boardworks Ltd 2003 EM Radiation: Uses: Dangers: Shadow pictures of luggage and inside the human body. High doses can kill cells. Lower doses can cause cells to become cancerous. X rays Hospital workers limit exposure to Gamma and X rays by standing behind lead shields or by leaving the room when the radiations are being used. How do hospital workers limit their exposure to Gamma and X rays?
© Boardworks Ltd 2003 X rays X rays can penetrate soft tissue but not b_____. X rays are a_______ more by some materials than others. P________ f____ is used to detect X rays. one bsorbed hotographic ilm How are X rays slides formed?
© Boardworks Ltd 2003 EM Radiation: Uses: Dangers: Sun beds, fluorescent lamps and security marking. High doses can kill cells. Lower doses can cause cells to become cancerous. Ultraviolet Which type of radiation is the most dangerous? The higher the frequency of the radiation, the more dangerous it is. So gamma is more dangerous than X rays or ultraviolet.
© Boardworks Ltd 2003 Effects of EM radiation on living cells Infra red radiation is used in toasters, grills and radiant heaters. What effect do you think it has on your skin? Ultraviolet radiation can pass through skin to deeper tissues. What effect do you think the colour of the skin has on the amount of radiation that passes through it? The darker the skin, the more ultraviolet radiation is absorbed, the less can reach into deeper soft tissues.
© Boardworks Ltd 2003 EM Radiation: Uses: Dangers: Seeing and endoscopes Blindness Light
© Boardworks Ltd 2003 EM Radiation: Uses: Dangers: Remote controls (TV/VCR), radiant heaters, grills, optical fibre communication, night vision. Skin burns Infrared
© Boardworks Ltd 2003 Night vision All objects above absolute zero emit infrared radiation. The hotter an object is, the more heat radiation it emits. Some animals and cameras can detect infrared radiation and are able to build up a heat picture. Which are the hottest/coolest parts of the image shown? light is hot dark is cold
© Boardworks Ltd 2003 EM Radiation: Uses: Dangers: Satellite communication, mobile phone networks, cooking, RADAR. Internal tissue heating. Microwaves
© Boardworks Ltd 2003 Microwaves Microwaves can be used in c_____ because many foods contain w____ molecules. Microwaves of the right w________ are able to make the water molecules r_______. This causes the food to get h____. How do microwaves cook foods? ooking ater avelength esonate otter
© Boardworks Ltd 2003 EM Radiation: Uses: Dangers: Communication and astronomy. Radio waves
© Boardworks Ltd 2003 Radio waves How do radio signals from the UK reach around the globe? The longer wavelength radio waves from a transmitter reflect off the Earths outer atmosphere (ionosphere).
© Boardworks Ltd 2003 How can houses in the shadows of hills receive a radio signal? All electromagnetic radiation travels in straight lines, does it not? Remember diffraction?Radio waves diffract around the hill to the house. Radio waves
© Boardworks Ltd 2003 Getting hotter If electromagnetic radiation is incident upon a material what effects could it have? An alternating current could be induced in the material, with the same frequency as the incident radiation. The temperature of the material could increase. 21º C30º C50º C70º C
© Boardworks Ltd 2003 EM Questions 1)Match up the following parts of the electromagnetic spectrum with their uses : Gamma raysAllow us to see Radio wavesRemote Controls Ultra VioletSee broken bones VisibleCarry TV signals MicrowavesRADAR X raysSterilise equipment Infra RedCauses sun-tans
© Boardworks Ltd 2003 EM Questions 2) Which radiations are missing from below? Gamma AUltravioletLightInfrared BRadio waves A.___________ B.___________ X rays Microwaves
1 IGCSE Physics Waves. 2 Lesson 4 – The EM Spectrum Aims: To understand that light is part of a continuous electromagnetic spectrum which includes radio,
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© Boardworks Ltd of 30. © Boardworks Ltd of 30.
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© Boardworks Ltd of 20 © Boardworks Ltd of 47 KS3 Physics 8K Light.
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