EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 3-2 Using Waves (The Electromagnetic Spectrum)

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

2. 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 Edexcel Specification 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: LONGEST WAVELENGTH SHORTEST WAVELENGTH RADIO WAVES MICROWAVES INFRA-RED VISIBLE LIGHT ULTRA-VIOLET X-RAYS GAMMA RAYS

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

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 (300 000 000 m/s) 4. They can all be reflected, refracted and diffracted** Notes: (a) 300 000 00 m/s is the same as 186 000 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 300 000 000 m/s. wave speed (v)=frequency (f)xwavelength (λ) becomes: λ=v÷f = 300 000 000 m/s ÷ 100 MHz = 300 000 000 m/s ÷ 100 000 000 Hz wavelength = 3.0 metres

8. Question 2 Calculate the frequency of a light wave of wavelength 0.000 7mm of speed 300 000 000 m/s. v=fxλ becomes: f=v÷λ = 300 000 000 m/s ÷ 0 000 7 mm = 300 000 000 m/s ÷ 0 000 000 7 m frequency = 429 000 000 000 000 Hz (or = 4.29 x 1014 Hz)

9. Complete: Answers highest frequency longest wavelength greatest energy GAMMA RADIO GAMMA X-RAYS MICROWAVES X-RAYS ULTRAVIOLET ULTRAVIOLET INFRA-RED VISIBLE LIGHT VISIBLE LIGHT VISIBLE LIGHT INFRA-RED ULTRAVIOLET INFRA-RED MICROWAVES X-RAYS MICROWAVES RADIO GAMMA RADIO 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 __________, 300 000 000 m/s. spectrum seven shortest energy ultraviolet microwaves speed vacuum WORD SELECTION: ultraviolet shortest energy spectrum vacuum speed seven microwaves

11. Radio and television both use radio waves Radio waves

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

13. MRI scanner and scan Radio telescope 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

14. transmitter receiver radio wave 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.

15. TRIPLE ONLY Diffraction out of a gap Diffraction around an obstacle 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.

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

18. 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. Radio waves and the ionosphere

19. Two uses of microwaves Microwaves

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

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

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

24. RADIO MICROWAVES INFRA-RED LIGHT ULTRA-VIOLET X-RAYS Infra-red photograph. brighter = hotter GAMMA RAYS 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.

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 _________. longer emitted temperature centimetres cooking lowest galaxy WORD SELECTION: emitted lowest galaxy cooking temperature longer centimetres

27. Visible light

28. Visible light is emitted from hot objects like the Sun. Visible light has wavelengths ranging from: 0.000 000 4m (violet) to 0.000 000 7m (red). RADIO RED MICROWAVES ORANGE INFRA-RED YELLOW LIGHT GREEN ULTRA-VIOLET BLUE X-RAYS INDIGO GAMMA RAYS VIOLET 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 Security markings show up under ultraviolet light Ultraviolet emitted by the Sun Fluorescent lamps and energy efficient bulbs work using uv

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

34. X-rays X-ray photographs Exploding 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. dangerous mutation cancer lead bones bacteria sterilise WORD SELECTION: bones mutation cancer bacteria lead dangerous sterilise

44. TRIPLE ONLY Communication With Waves

45. TRIPLE ONLY 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.

46. ANALOGUE DIGITAL TRIPLE ONLY Examples of analogue and digital systems

47. TRIPLE ONLY Regenerator ‘Noisy’ pulse in ‘Clean’ pulse out Advantages of using digital signals • 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.

48. TRIPLE ONLY 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!

49. Sequential Puzzle on EM Spectrum Wavelength order- by KT - Microsoft WORD Sequential Puzzle on EM Spectrum Frequency order- by KT - Microsoft WORD Hidden Pairs Game on EM Spectrum Uses - by KT - Microsoft WORD Electromagnetic Spectrum bounce quiz - eChalk Radio 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. Microwaves - 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 Pictures - falstad The 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. Online Simulations Making X-rays - Colorado X-rays - Fluoroscope demo - Colorado Fibre optic reflection - NTNU BBC AQA GCSE Bitesize Revision: What is a spectrum The electromagnetic spectrum - table Radio waves Microwaves UV & IR Gamma & X-rays Hazards of radiation Optical fibres Analogue & digital signals Comaparing analogue & digital

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