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EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 3-2 Using Waves (The Electromagnetic Spectrum) Edexcel IGCSE Physics pages 99 to 106 June 17 th 2012 Content applying.

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Presentation on theme: "EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 3-2 Using Waves (The Electromagnetic Spectrum) Edexcel IGCSE Physics pages 99 to 106 June 17 th 2012 Content applying."— Presentation transcript:

1 EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 3-2 Using Waves (The Electromagnetic Spectrum) Edexcel IGCSE Physics pages 99 to 106 June 17 th 2012 Content applying to Triple Science only is shown in red type on the next slide and is indicated on subsequent slides by ‘ TRIPLE ONLY ’

2 Edexcel Specification Section 3: Waves c) The electromagnetic spectrum understand that light is part of a continuous electromagnetic spectrum which includes radio, microwave, infrared, visible, ultraviolet, x-ray and gamma ray radiations and that all these waves travel at the same speed in free space identify the order of the electromagnetic spectrum in terms of decreasing wavelength and increasing frequency, including the colours of the visible spectrum explain some of the uses of electromagnetic radiations, including: radio waves: broadcasting and communications microwaves: cooking and satellite transmissions infrared: heaters and night vision equipment visible light: optical fibres and photography ultraviolet: fluorescent lamps x-rays: observing the internal structure of objects and materials and medical applications gamma rays: sterilising food and medical equipment understand the detrimental effects of excessive exposure of the human body to electromagnetic waves, including: microwaves: internal heating of body tissue infra-red: skin burns ultraviolet: damage to surface cells and blindness gamma rays: cancer, mutation. and describe simple protective measures against the risks. d) Light and sound understand the difference between analogue and digital signals describe the advantages of using digital signals rather than analogue signals describe how digital signals can carry more information Red type: Triple Science Only

3 The Electromagnetic Spectrum The electromagnetic spectrum is a continous spectrum of waves which includes the visible spectrum.

4 The electromagnetic spectrum is divided into seven bands which in order of decreasing wavelength are: GAMMA RAYS X-RAYS ULTRA-VIOLET INFRA-RED RADIO WAVES MICROWAVES VISIBLE LIGHT LONGEST WAVELENGTH SHORTEST WAVELENGTH

5 Listing in order of decreasing frequency and energy: GAMMA RAYS X-RAYS ULTRA-VIOLET INFRA-RED RADIO WAVES MICROWAVES VISIBLE LIGHT HIGHEST FREQUENCY LOWEST FREQUENCY GREATEST ENERGY LEAST ENERGY

6 Common properties All electromagnetic waves, including visible light have the following common properties: 1. They transfer energy 2. They are all transverse waves 3. They all travel at the same speed through a vacuum ( m/s) 4. They can all be reflected, refracted and diffracted** Notes: (a) m/s is the same as miles per second. (b) Through air, light and the other waves travel at about the above speed but through denser substances (for example glass) the speed falls. (c) According to Albert Einstein’s Theory of Relativity nothing can travel faster than the speed of light through a vacuum. (d) ** Double Science students do not need to know about diffraction

7 Question 1 Calculate the wavelength of a radio wave in of frequency 100 MHz if its speed is m/s. wave speed (v) = frequency (f) x wavelength (λ) becomes: λ = v ÷ fλ = v ÷ f = m/s ÷ 100 MHz = m/s ÷ Hz wavelength = 3.0 metres

8 Question 2 Calculate the frequency of a light wave of wavelength mm of speed m/s. v = f x λv = f x λ becomes: f = v ÷ λf = v ÷ λ = m/s ÷ mm = m/s ÷ m frequency = Hz (or = 4.29 x Hz)

9 Complete: Answers GAMMA X-RAYS ULTRAVIOLET VISIBLE LIGHT INFRA-RED MICROWAVES RADIOGAMMA X-RAYS ULTRAVIOLET VISIBLE LIGHT INFRA-RED MICROWAVES RADIOGAMMA X-RAYS ULTRAVIOLET VISIBLE LIGHT INFRA-RED MICROWAVES RADIO highest frequency longest wavelength greatest energy lowest frequency shortest wavelength least energy

10 Choose appropriate words to fill in the gaps below: The electromagnetic __________ is a group of waves that are divided into ________ bands. Gamma rays have the ________ wavelength, highest frequency and ________. The rest of the spectrum, in order of increasing wavelength are: x-rays, _________, visible light, infra-red, ___________ and radio waves. All electromagnetic waves travel at the same _______ through a __________, m/s. vacuum seven shortest ultraviolet microwaves energyspectrum WORD SELECTION: speed vacuum seven shortest ultravioletmicrowaves energy spectrum speed

11 Radio waves Radio and television both use radio waves

12 Radio waves have the longest wavelengths of the electromagnetic spectrum, typically 100 metres. RADIO MICROWAVES INFRA-RED LIGHT ULTRA-VIOLET X-RAYS GAMMA RAYS A radio transmitter

13 Uses of radio waves Radio waves are used in: radio and television communication medicine with MRI scanners astronomy to ‘see’ the centre of our galaxy MRI scanner and scan Radio telescope

14 receiver Transmitting and receiving radio waves Radio waves are emitted from a transmitter aerial when an alternating voltage is connected to the aerial. The radio wave emitted has the same frequency as the alternating voltage. When these radio waves pass across a receiver aerial, they cause a tiny alternating voltage of the same frequency to occur in the aerial. radio wave transmitter

15 Diffraction Diffraction occurs when a wave spreads out from a gap or bends around an obstacle. Diffraction is more significant with low frequency, long wavelength waves. Diffraction results in the energy of the wave spreading out. Diffraction out of a gap Diffraction around an obstacle TRIPLE ONLY

16 Radio frequency bands The radio and microwave part of the electromagnetic spectrum is sub- divided into frequency bands. The uses of each band depends on its frequency range. The higher the frequency: The more information that can be carried – this can result in better quality sound and video or more channels. The shorter their range – due to greater absorption by the atmosphere. The less the signal spreads out – less diffraction – hills and large buildings also are more likely to stop the signal. Higher frequency waves are less able to diffract around buildings and hills

17 Wavebands WavebandFrequency rangeUses Microwaves UHF (ultra-high frequency) VHF (very-high frequency) HF (high frequency) also called ‘short wave’ or SW MF (medium frequency) also called ‘medium wave’ or MW LF (low frequency) also called ‘long wave’ or LW VLF (very-low frequency) greater than 3 GHz (wavelength less than 10 cm) 300 MHz – 3 GHz (wavelengths: cm) 30 MHz – 300 MHz (wavelengths: m) 300 kHz – 3 MHz (wavelengths: 100 – 1000 m) 30 kHz – 300 MHz (wavelengths: 1 – 10 km) less than 30 kHz (wavelengths more than 10 km) 3 MHz – 30 MHz (wavelengths: 10 – 100 m) Satellite TV Mobile phones Terrestrial TV Mobile phones FM radio Emergency services Digital radio Amateur radio International radio (AM) National radio (AM) International radio (AM) Submarine communication Note: 1 GHz = 1000 MHz; 1 MHz = 1000 kHz; 1 kHz = 1000 Hz

18 Radio waves and the ionosphere The ionosphere is a layer of gas in the upper atmosphere that reflects radio waves of frequencies less than about 30 MHz. Radio waves can be reflected off the bottom of the ionosphere enabling them to travel great distances. The ionosphere is stronger in summer than winter and so distant radio stations can be received better in summer. Before the advent of satellites, using the ionosphere was one of the main ways of communicating around the world.

19 Microwaves Two uses of microwaves

20 Microwaves have wavelengths of typically 10 cm. Microwave transmitter / receiver used for a mobile phone network. RADIO MICROWAVES INFRA-RED LIGHT ULTRA-VIOLET X-RAYS GAMMA RAYS

21 Uses of microwaves Microwaves are used for: cooking mobile phone communication satellite television astronomy – finding out about the origin of the Universe Cosmic Microwave Background Radiation Satellite television receiver

22 Dangers of microwaves Microwaves can cause internal heating of body tissue. Microwave ovens contain metal shielding to prevent the microwaves from leaking out. Some people believe that over use of mobile phones can lead to brain damage.

23 Infra-red radiation Despite appearances this heater is giving off mostly invisible infra-red radiation. An infra-red or thermal image. RED = hot BLUE = cold

24 Infra-red waves have wavelengths of typically a millionth of a metre (1 micrometre) They are emitted by all objects. The hotter the object, the more infra-red radiation is emitted. RADIO MICROWAVES INFRA-RED LIGHT ULTRA-VIOLET X-RAYS GAMMA RAYS Infra-red photograph. brighter = hotter

25 Uses of infra-red Infra-red waves are used: to cook food by remote controls in communication systems using optical fibres to detect intruders in burglar alarms in ‘night sights’ in astronomy to see behind gas clouds

26 Choose appropriate words to fill in the gaps below: Infra-red radiation has a _________ wavelength than visible light and is _________ by all objects. The higher the ___________ of an object the greater is the amount of IR radiation emitted. Microwaves have wavelengths of a few ___________ and are used for ________ and communication. Radio waves have the longest wavelengths but the ________ frequencies of the electromagnetic spectrum. Radio waves are used to study the centre of our _________. lowestcentimetrescookinglongertemperaturegalaxy WORD SELECTION: emitted lowest centimetres cooking longer temperature galaxy emitted

27 Visible light

28 Visible light is emitted from hot objects like the Sun. Visible light has wavelengths ranging from: m (violet) to m (red). RADIO MICROWAVES INFRA-RED LIGHT ULTRA-VIOLET X-RAYS GAMMA RAYS VIOLET INDIGO BLUE GREEN YELLOW ORANGE RED White light can be split into the colour spectrum using a prism or with water.

29 Uses of visible light Visible light is used: for sight in photography in optical fibres in photosynthesis

30 Ultraviolet Ultraviolet emitted by the Sun Fluorescent lamps and energy efficient bulbs work using uv Security markings show up under ultraviolet light

31 Ultraviolet has a wavelength of typically of a ten millionth of a metre. UV is produced from very hot objects like the Sun or from special electrical tubes. Most of the Sun’s ultraviolet radiation is absorbed by the Ozone layer in the upper part of the Earth’s atmosphere. UV is also stopped by glass. RADIO MICROWAVES INFRA-RED LIGHT ULTRA-VIOLET X-RAYS GAMMA RAYS

32 Uses of ultraviolet Ultraviolet is used in: Fluorescent lamps including energy efficient light bulbs Security devices Dentistry Pest control Astronomy A bird appears on many Visa credit cards when held under a UV light source Ultraviolet light used in cosmetic dentistry ‘zapper’ attracts insects using uv

33 Safety with ultraviolet The Sun’s ultraviolet light is responsible for sun tan. Too much exposure to UV can cause blindness and skin cancer. 5 use a high sun protection factor sunscreen – reapply after swimming 1 wear a hat 3 cover up when the Sun is strongest 4 longer shorts offer protection sunglasses with UV protection 2

34 X-rays X-ray photographsExploding stars emit X-rays

35 X-rays have wavelengths of typically a billionth of a metre. They are produced from X-ray tubes that use very high voltage (typically one hundred thousand volts). They are very penetrating and are only stopped by several centimetres of lead. RADIO MICROWAVES INFRA-RED LIGHT ULTRA-VIOLET X-RAYS GAMMA RAYS

36 Uses of X-rays X-rays are used in: X-ray photographs Airport security Cancer treatment Astronomy

37 Taking an X-ray (radiograph) X-rays pass through soft tissue but are absorbed by bones. X-rays are directed onto the patient from the X-ray tube. A light proof cassette containing a photographic film is placed on the other side of the patient. A patient being prepared for a radiograph

38 When the X-ray tube is switched on, the X-rays pass through the patient’s body leaving a ‘shadow’ image on the film showing the bones. When the film is developed the parts exposed by the X-rays are darker than the other parts. The bones show up as lighter regions on the radiograph. A chest X-ray

39 Gamma Rays Gamma rays are given off by nuclear explosions Gamma rays are emitted from material falling into black holes

40 Gamma Rays Gamma rays have the shortest wavelengths of the electromagnetic spectrum, typically a millionth millionth of a metre. They are emitted by radioactive substances. They are very penetrating and are only stopped by several centimetres of lead. RADIO MICROWAVES INFRA-RED LIGHT ULTRA-VIOLET X-RAYS GAMMA RAYS

41 Uses of gamma rays Gamma rays are used: to kill cancer cells to kill harmful bacteria in food to sterilise surgical instruments Gamma rays being used to treat cancer

42 Safety with gamma and X-rays Too much exposure to gamma rays or X-rays is dangerous. High doses kill living cells. Low doses cause cell mutation and cancerous growth. Workers who use equipment producing gamma or X-rays wear a film badge called a dosemeter. The film in the badge darkens if the person receives a too high dosage of radiation. a dosemeter

43 Choose appropriate words to fill in the gaps below: Gamma and X-rays are the most _________ radiations of the electromagnetic spectrum. Both can cause cell _________ and cancerous growth although both can also be used to treat ________. Both require several centimetres of ______ to be stopped. X-rays are absorbed by ______ allowing the production of radiographs. Gamma rays are used to kill _________ in food and to _________ medical instruments. bacteriacancermutation dangerous bones sterilise WORD SELECTION: lead bacteria cancer mutation dangerous bones sterilise lead

44 Communication With Waves TRIPLE ONLY

45 Analogue and digital signals Communication signals may be analogue or digital. Analogue signals vary continuously in amplitude between zero and some maximum level. Digital signals only have two voltage levels, for example +5V and 0V. TRIPLE ONLY

46 Examples of analogue and digital systems ANALOGUEDIGITAL TRIPLE ONLY

47 Advantages of using digital signals 1. Less interference than with analogue signals. Interference causes a hissing noise with analogue radio. This does not happen with digital signals because regenerator circuits are used to clean ‘noisy’ pulses. So a digital signal has a higher quality than an analogue one. Regenerator ‘Noisy’ pulse in ‘Clean’ pulse out TRIPLE ONLY

48 2. Much more information can be sent. Digital pulses can be made very short so more pulses can be carried each second. Different signals can be sent together by a process called multiplexing. 3. Digital signals are easily processed by computers. Computers are digital devices! TRIPLE ONLY

49 Online Simulations Sequential Puzzle on EM Spectrum Wavelength order- by KT - Microsoft WORDEM Spectrum Wavelength Sequential Puzzle on EM Spectrum Frequency order- by KT - Microsoft WORDEM Spectrum Frequency Hidden Pairs Game on EM Spectrum Uses - by KT - Microsoft WORDEM Spectrum Uses Electromagnetic Spectrum bounce quizElectromagnetic Spectrum bounce quiz - eChalk Radio Waves & Electromagnetic FieldsRadio Waves & Electromagnetic Fields - PhET - Broadcast radio waves from KPhET. Wiggle the transmitter electron manually or have it oscillate automatically. Display the field as a curve or vectors. The strip chart shows the electron positions at the transmitter and at the receiver. MicrowavesMicrowaves - PhET - How do microwaves heat up your coffee? Adjust the frequency and amplitude of microwaves. Watch water molecules rotating and bouncing around. View the microwave field as a wave, a single line of vectors, or the entire field. Thermal Camera PicturesThermal Camera Pictures - falstad The Greenhouse EffectThe Greenhouse Effect - PhET - Just how do greenhouse gases change the climate? Select the level of atmospheric greenhouse gases during an ice age, in the year 1750, today, or some time in the future and see how the Earth's temperature changes. Add clouds or panes of glass. Making X-raysMaking X-rays - Colorado X-raysX-rays - Fluoroscope demo - Colorado Fibre optic reflectionFibre optic reflection - NTNU BBC AQA GCSE Bitesize Revision: What is a spectrum The electromagnetic spectrumThe electromagnetic spectrum - table Radio waves Microwaves UV & IR Gamma & X-rays Hazards of radiation Optical fibres Analogue & digital signals Comaparing analogue & digital

50 Using Waves Notes questions from pages 99 to Copy the table on page Give five common properties of all members of the electromagnetic spectrum. (see page 99) 3.List the colours of the visible spectrum in order of increasing wavelength. (see page 102) 4.State the hazards of (a) microwaves; (b) ultra-violet; (c) X-rays and gamma rays. (see pages 101 to 103) 5.(a) Explain the difference between analogue and digital signals. (b) What are the advantages of using digital signals? (see pages 104 and 105) 6.Answer the questions on page Verify that you can do all of the items listed in the end of chapter checklist on page 106. TRIPLE ONLY

51 Using Waves Notes questions from pages 99 to Copy the table on page Give five common properties of all members of the electromagnetic spectrum. (see page 99) 3.List the colours of the visible spectrum in order of increasing wavelength. (see page 102) 4.State the hazards of (a) microwaves; (b) ultra- violet; (c) X-rays and gamma rays. (see pages 101 to 103) 5.Answer questions 1 and 2 on page 106. DOUBLE SCIENCE ONLY


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