AQA GCSE 1b-5b Electromagnetic Waves Part B – IR, Microwaves, Radio, Communications & Signals

1. AQA GCSE 1b-5bElectromagnetic WavesPart B – IR, Microwaves, Radio, Communications & Signals AQA GCSE Physics pages 84 to 93 AQA GCSE Science pages 288 to 297 September 15th 2010

2. AQA GCSE Specification THE ELECTROMAGNETIC SPECTRUM 11.5 What are the uses and hazards of the waves that form the electromagnetic spectrum? Using skills, knowledge and understanding of how science works: • to evaluate the possible hazards associated with the use of different types of electromagnetic radiation Skills, knowledge and understanding of how science works set in the context of: • When radiation is absorbed the energy it carries makes the substance which absorbs it hotter and may create an alternating current with the same frequency as the radiation itself. • The uses and the hazards associated with the use of each type of radiation in the electromagnetic spectrum. • Radiowaves, microwaves, infra red and visible light can be used for communication. • Microwaves can pass through the Earth’s atmosphere and are used to send information to and from satellites and within mobile phone networks. • Infra red and visible light can be used to send signals along optical fibres and so travel in curved paths. • Communication signals may be analogue (continuously varying) or digital (only on and off). Digital signals are less prone to interference than analogue and can be processed by computers

3. 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

4. GAMMA X-RAYS ULTRAVIOLET LIGHT INFRA-RED MICROWAVES RADIO Infra-red (IR) Infra-red waves have wavelengths of typically 1 micrometre. (0.000 001 m, a millionth of a metre). They are emitted by all objects. The hotter the object, the more infra-red radiation is emitted.

5. 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

6. Two uses of microwaves Microwaves

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

8. 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

9. Radio and television both use radio waves Radio waves

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

11. 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.

12. 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

13. 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

14. 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. Fibre optic reflection - NTNU BBC Bitesize Revision: Optical fibres Microwave Ovens - Colorado 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. 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. Find the nearest radio masts - Ofcom Simplified MRI Scanner - PhET - Is it a tumor? Magnetic Resonance Imaging (MRI) can tell. Your head is full of tiny radio transmitters (the nuclear spins of the hydrogen nuclei of your water molecules). In an MRI unit, these little radios can be made to broadcast their positions, giving a detailed picture of the inside of your head. BBC Bitesize Revision: Ultraviolet & Infra-red Microwaves Radio waves Simulations

15. Infra-red, microwaves and radio wavesNotes questions from pages 84/288 & 85/289 • What type of objects emit infra-red radiation? How can infra-red radiation be dangerous? • Why are microwaves so called? • Write a sentence in each case about four uses of infra-red radiation and two uses of microwaves. • Copy and answer questions (a) and (b) on page 84/288. • State the frequency range of radio waves and how they compare with microwaves. • Explain what happens in an aerial when radio waves are (a) transmitted and (b) received. • Copy the Key Points on page 85/289. • Answer the summary questions on page 85/289.

16. In text questions: Between light and microwaves (i) Yes (ii) They cause the microwave oven to overheat, because metal objects absorb microwave radiation very easily. Summary questions: (a) Radio waves, light (b) Microwaves, infra-red radiation. (a) Infra-red (b) Microwave (c) Radio (d) Infra-red 3. An alternating voltage applied to an aerial produces radio waves which cause a small alternating voltage in the receiver aerial when they arrive there. Infra-red, microwaves and radio wavesANSWERS

17. Communications

18. 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.

19. 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

20. 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

21. 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

22. Optical fibre communication Optical fibres are very thin glass fibres. They can be used to transmit information using visible light or infra-red radiation. The light cannot escape from the fibre, it is continually reflected internally by the fibre. Compared with microwaves and radio waves optical fibres: • can carry far more information due to the higher frequency of light and infra-red. • are more secure because the signals stay within the fibres. The fastest broadband uses optical fibres.

23. Choose appropriate words to fill in the gaps below: Communication systems make use of visible light, infra-red, ___________ and radio waves. The higher the __________ of the wave used, the greater the amount of __________ that can be transmitted in the same time. Satellite television and _________ phone networks therefore uses high frequency microwaves to allow for many _________. Lower frequency radio waves, however, allow long ________ communication without the need to use _________. microwaves frequency information mobile channels distance satellites WORD SELECTION: microwaves mobile channels satellites information distance frequency

24. TV Screens - Colorado Fibre optic reflection - NTNU BBC Bitesize Revision: Optical fibres 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. Find the nearest radio masts - Ofcom Electromagnetic Spectrum & Communications - BT Analogue & Digital Signals - BT Multiplexing - BT Fibre optic reflection - NTNU Inside a communication satellite - BT BBC Bitesize Revision: Introduction Page to AQA Sending Information Optical fibres Recognising Analogue & Digital Signals Comparing Analogue & Digital Signals - includes an applet showing how noise affects the two types of signal Test bite on Sending Information Communications Simulations

25. Communications Notes questions from pages 86/290 & 87/291 • Copy out the waveband table on page 86/290. • Why is the quality of communication better with the higher frequency radio bands? • Draw a diagram and explain how the ionosphere is used in radio communication. • What are optical fibres? Draw a diagram showing how light travels through an optical fibre. • What advantages does optical fibre communication have over radio wave communication? • Copy and answer questions (a), (b), (c) and (d) on pages 86/290 and 87/291. • Copy the Key Points on page 87/291. • Answer the summary questions on page 87/291.

26. In text questions: Satellite TV signals are from a transmitter on a satellite; terrestrial TV signals are from transmitters on the ground. The signals pass into space because they do not reflect from the ionosphere. The signals go straight through the atmosphere above you and into space. Optical fibres are only suitable for fixed links. Summary questions: (a) Radio waves (b) Microwaves (c) Microwaves, radio waves. 2. (a) Local radio stations transmit radio waves that are easily absorbed by the atmosphere so they can’t travel far. (b) The signals are carried by light or infra-red radiation, which can’t be detected outside the fibre surface because it only enters or leaves at its ends. 3. Because microwaves are not reflected by the ionosphere. They pass straight through. Communications ANSWERS

27. 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.

28. ANALOGUE DIGITAL Examples of analogue and digital systems

29. 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.

30. 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!

31. Electromagnetic Spectrum & Communications - BT Analogue & Digital Signals - BT BBC Bitesize Revision: Introduction Page to AQA Sending Information Optical fibres Recognising Analogue & Digital Signals Comparing Analogue & Digital Signals - includes an applet showing how noise affects the two types of signal Test bite on Sending Information Analogue and Digital Signals Simulations

32. Analogue and digital signalsNotes questions from pages 88/292 & 89/293 • Define what is meant by a (a) digital signal and (b) analogue signal. Copy Figure 1 on page 88/292 below your answers. • Give some examples of both types of signal. • Explain the advantages of using digital signals in communication. • Explain what is meant by: (a) a carrier wave, (b) amplitude modulation and (c) frequency modulation. • Copy and answer questions (a), (b) and (c) on pages 88/292 and 89/293. • Copy the Key Points on page 89/293. • Answer the summary questions on page 89/293.

33. In text questions: To convert an analogue signal into a digital signal. Digital. Digital. Summary questions: (a) Analogue, carrier. (b) digital, analogue. (c) Digital. A: carrier wave, B: signal, C: transmitter, D: receiver. 3. Analogue to digital: The voltage of the analogue waveform is ‘sampled’ (that is measured) automatically many times each second. Each voltage measurement is then turned electronically into a corresponding sequence of pulses. The digital signal consists of successive pulse sequences (that is a digital signal). Digital to Analogue: Each sequence of pulses of the digital signal is turned into a corresponding analogue voltage measurement. The analogue waveform consists of successive analogue voltage measurements. Analogue and digital signalsANSWERS

34. Microwave issuesNotes questions from pages 90/294 & 91/295 • Answer question 1 on page 90/294. • Answer question 2 on page 91/295.

35. Microwave issuesANSWERS • The higher the power the longer the range. Submarines could be detected further away using high power radar. • (a) Microwave radiation penetrates their skulls more than older skulls because their skulls are thinner. Also, smaller heads heat up more easily than bigger heads. (b) They could find out if people with brain tumours used mobile phones (e.g. average use per day per person) more than the average healthy person. (c) They could use a brain scanner to compare the brains of people who used mobile phones a lot with ‘non-users’. They could conduct other tests as well, such as memory tests. They could also compare the brains of dead rats exposed to microwaves with those of unexposed rats. (d) The driver needs to concentrate on driving and is distracted by using a mobile phone at the same time.

36. How Science WorksANSWERS • The longer the wavelength of light the higher the voltage. • The reading after 80 seconds. • The anomaly should be investigated further. • A line graph. Both variables are continuous.