SP11. StudyPacks KS4 SCIENCE STUDY. Electromagnetic Waves. Uses and Dangers

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1 StudyPacks STUDY. KS4 SCIENCE Electromagnetic Waves Uses and Dangers This Study Pack aims to cover:. The uses and dangers of Electromagnetic waves.. SP Study Packs are prepared by Qualified Teachers and Specialists and are a complete range of comprehensive compiled resources based on the UK National Curriculum covering the Primary and Secondary Frameworks including SATs and GCSE examinations. Student Name

2 Contents Electromagnetic Waves 2-3 Practice questions 4-7 Exam questions 8-28 Mark scheme 29-32

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5 The electromagnetic spectrum Notes The electromagnetic spectrum is a continuous range of wavelengths. The types of radiation that occur in different parts of the spectrum have different uses and dangers, which depend on their wavelength and frequency. Refraction from a prism White light can be split up using a prism to form a spectrum. The light waves are refracted as they enter and leave the prism. The shorter the wavelength of the light, the more it is refracted. As a result, red light is refracted the least and violet light is refracted the most, causing the coloured light to spread out to form a spectrum. Visible light is just one type of electromagnetic radiation. There are various types of electromagnetic radiation, some with longer wavelengths than visible light and some with shorter wavelengths than visible light. The electromagnetic spectrum Electromagnetic waves form a continuous spectrum. You should know the order of electromagnetic waves in the spectrum as shown in the table below. The main types of electromagnetic radiation 4

6 energy frequency wavelength type of electromagnetic radiation typical use lowest lowest longest radio waves television signals microwaves cooking, mobile phones infrared optical fibre communication visible light seeing ultraviolet detecting forged bank notes X-rays medical images of bones highest highest shortest gamma radiation killing cancer cells Radio waves have the lowest frequencies and longest wavelengths, while gamma waves have highest frequencies and shortest wavelengths. The wavelengths vary across the electromagnetic spectrum from about 0 5 m to more than 04 m. Communicating with waves: radio waves and microwaves Radio waves, microwaves, visible light and infrared can all be used for communication. You should know some typical examples of these, and associated hazards. Radio waves Radio waves are used to transmit television and radio programmes. Television uses higher frequencies than radio. A radio programme receiver does not need to be directly in view of the transmitter to receive programme signals. Diffraction allows low-frequency radio waves to be received behind hills, although repeater stations are often used to improve the quality of the signals. The lowest frequency radio waves are also reflected from an electrically charged layer of the upper atmosphere, called the ionosphere. This means that they can still reach receivers that are not in the line of sight because of the curvature of the Earth's surface. Microwaves and radio waves in the atmosphere 5

7 Microwaves A mobile phone mast - an example of a microwave transmitter Microwave radiation can also be used to transmit signals such as mobile phone calls. Microwave transmitters and receivers on buildings and masts communicate with the mobile telephones in their range. Some people think that mobile phones, which transmit and receive microwaves, may be a health risk. This is not accepted by everyone, as the intensity of the microwaves is too low to damage tissues by heating, and microwaves are not ionising. Certain microwave radiation wavelengths pass through the Earth's atmosphere and can be used to transmit information to and from satellites in orbit. Satellite television signals use microwaves Communicating with waves: visible light and infrared Radio waves, microwaves, visible light and infrared can all be used for communication. You should know some typical examples of these, and associated hazards. Visible light Visible light is the light we can see. It allows us to communicate with one another through books, hand signals and video, for example. The use of visible light needs the transmitter and receiver to be in the line of sight. But it is more secure against eavesdroppers than radio waves. Cameras let us record still pictures and movies, and photography is an important use of visible light. Very bright light can damage our eyes you should never look directly into the Sun. Infrared Optical fibres We cannot see infrared radiation, but we can feel it as heat energy. High intensity infrared is used in heaters, toasters and grills, and it can cause burns. Infrared sensors can detect heat from the body. They are used in: security lights burglar alarms. Infrared radiation is also used to transmit information from place to place, including: remote controls for television sets and DVD players data links between computers. 6

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15 ELECTROMAGNETIC WAVES Name of wave Uses Dangers Radio wave Microwave Infrared waves Light waves Ultraviolet waves x-rays Gamma 4

16 Communicate - stay in touch Aims Electromagnetic waves are all around us. They are how we communicate over short and long distances. After completing this worksheet, you should know the order of the parts of the spectrum, some of their properties and how microwaves and radio waves interact with the ionosphere. Questions.The table below shows some parts of the electromagnetic spectrum drawn by a student. The parts of the spectrum and values of the wavelengths are placed in the wrong order. Short wavelength microwaves radio waves ultraviolet infrared gamma rays X-rays Long wavelength visible 0 3 m 0-4 m 0-0 m 0-8 m 0-2 m 0-6 m 0-5 m a)in the table below, place the parts of the electromagnetic spectrum in the correct order. Give the correct wavelengths in the boxes below. Remember 0-4 is smaller than 0-0. Small wavelength Long wavelength radio waves 0 3 m Bi) Every part of the electromagnetic spectrum travels at a speed of 3.0 x 0 8 m/s in a vacuum. Name two other properties common to all electromagnetic waves. ii State which type of electromagnetic wave has the highest energy. 5

17 iii Radio waves have longer wavelengths than microwaves. Rearrange the following formula and use the numbers in your answer to part a above to show that microwaves have a higher frequency than radio waves. wave speed = frequency wavelength 2.The table gives information about some radio waves and microwaves. The ionosphere is a layer of the Earth s atmosphere which changes constantly in its ability to reflect some radio waves. Wave name Frequency range Effect of ionosphere microwaves above 3000 MHz passes through ultra-high frequency radio (UHF) MHz passes through very high frequency radio (VHF) MHz reflects high frequency radio (HF) 2 30 MHz reflects a On the diagram show, what happens to the HF radio wave as it hits the ionosphere. the position of a satellite used to transmit t.v. pictures to Earth. a microwave travelling from the satellite to the Earth. b)use the table to decide what frequencies can be used to send a signal to the satellite. c)explain how it is possible to use HF radio to talk to someone on the other side of the Earth. 6

18 d)you are listening to an HF radio programme from another country. Suddenly the signal fades. Explain why this may have happened. e)infrared radiation emitted by the surface does not escape from the Earth. It is absorbed by the atmosphere. Explain the difference between absorption and reflection. f)where are microwaves used around the home for communication? Discussion The ozone layer is another layer in the atmosphere. It absorbs some of the Sun s ultraviolet radiation. The ozone layer started to decrease in size some years ago. What might happen if this continues? Some people confuse the loss of the ozone layer with greenhouse warming. What is the difference? 7

19 Exam Questions Q. The diagram below shows the range of wavelengths and frequencies for all the types of radiation in the electromagnetic spectrum. X rays, which have frequencies in the range Hz are already marked on the diagram. Complete the diagram by adding the following: (a) (b) (c) (d) (e) gamma radiation, which has shorter wavelengths than X rays; radio waves which have wavelengths longer than 0.m; the visible spectrum which has wavelengths from 400 nm (violet) to 700 nm (red); ultraviolet radiation (i.e. radiation with a higher frequency than violet light); microwaves which have a shorter wavelength than radio waves and infrared radiation which has a higher frequency than microwaves; (f) an FM radio programme on 92MHz. (Show this with an arrow ) (Total 7 marks) 8

20 Q2. Radio waves, ultra-violet, visible light and X-rays are all types of electromagnetic radiation. (a) Choose wavelengths from the list below to complete the table m 0 m m 500 m TYPE OF RADIATION WAVELENGTH (m) Radio waves Ultra-violet Visible light X-rays (4) (b) Microwaves are another type of electromagnetic radiation. Calculate the frequency of microwaves of wavelength 3 cm. (The velocity of electromagnetic waves is 3 08 m/s.) (4) (Total 8 marks) Q3. After a person is injured a doctor will sometimes ask for a photograph to be taken of the patient s bone structure, e.g. in the case of a suspected broken arm. (i) Which type of electromagnetic radiation would be used to take the photograph? () (ii) Describe the properties of this radiation which enable it to be used to photograph bone structure. (2) (Total 3 marks) 9

21 Q4. The diagram shows a small part of the electromagnetic spectrum divided into seven sections. The different properties of the waves in each section make them useful in different ways. The waves in which section, A, B, C, D, E, F or G, are: (a) used to send a signal to a satellite in space... () (b) used to communicate with a submarine under the water... () (c) used by a radio station to broadcast programmes around the world... () (d) the waves with the shortest wavelength?... () (Total 4 marks) Q5. (a) Scientific research carried out in 3 countries has tried to find out if there are any links between using a mobile phone and developing different types of cancer. About people, half with cancer and half in good health, were interviewed about their mobile phone use. (i) Suggest why people in good health were interviewed () 20

22 (ii) Interviewing people gave the researchers a large sample size. Give one advantage, in any research project, of having a large sample size rather than a small sample size () (b) The following information was included in a newspaper article about the research project. It may be difficult to prove there is a link simply by asking people how much they use a mobile phone. People s memories are not always accurate. Scientists in Israel found that people who use a mobile phone a lot are 50% more likely to develop a cancer on the salivary gland just in front of the ears. The cost of the research, 20 million, has been partly paid for by mobile phone companies. No children were included in the research. (i) Draw a ring around the correct answer to complete the following sentence. Using children in scientific research raises environmental ethical social issues. () (ii) Suggest two reasons why some people are concerned that the research was partly paid for by mobile phone companies (2) 2

23 (iii) In Germany, mobile phones that emit very low levels of radiation are marked with a special symbol. Explain why low emission mobile phones should be marked in this way (2) (Total 7 marks) Q6. The table shows the electromagnetic spectrum. Three types of wave have been missed out. (i) Use words from the box to complete the table. infra red rays radio waves X-rays (2) (ii) Which one of the following gives a use of gamma rays? Put a tick ( ) in the box next to your choice. to communicate with satellites to see objects to kill cancer cells () 22

24 (iii) Complete the following sentence by drawing a ring around the correct word in the box. energy All electromagnetic waves move gases from one place to another. particles () (Total 4 marks) Q7. (a) An endoscope is an instrument used by doctors for looking inside patients. A bundle of thin optical fibres pass light into the patient s body, a second bundle of fibres carry reflected light back to the doctor. (i) Complete the diagram below to show how an optical fibre is able to pass light into a patient s body. (2) (ii) Give one advantage of using lots of thin fibres to make the bundles, rather than a few thick fibres () (iii) Give one further example of the practical use of an optical fibre () 23

25 (b) The diagram shows a wave travelling through a stretched spring. In what way is this wave the same as a sound wave? () (c) Sound waves travel faster in liquids than in gases. Why? () (d) A bat uses ultrasound to find its way around. Explain how. (2) (Total 8 marks) Q8. The picture shows a horse being prepared for an X-ray. The person who will take the X-ray and the person holding the horse are wearing special aprons. These aprons have a lead lining. Explain why the lead lining is important. To gain full marks in this question you should write your ideas in good English. Put them into a sensible order and use the correct scientific words

26 (Total 3 marks) Q9. Both X-ray machines and CT scanners are used to produce images of the body. (a) The diagram shows an X-ray photograph of a broken leg. Before switching on the X-ray machine, the radiographer goes behind a screen. Explain why the radiographer does this (3) (b) The following is an extract from a newspaper article. X-rays cause 700 new cancers each year in the U.K. Each year there are about new cancer cases in the UK, of which, about 700 may be due to the use of X-rays to diagnose illness. The article was reporting on a scientific research project first published in a medical journal. What evidence would the scientists have collected to come to the conclusion that X-rays can cause cancer?

27 ... (2) (c) Explain the advantage of a CT scan compared to an X-ray (2) (Total 7 marks) Q0. (a) Microwaves are one type of electromagnetic wave. (i) Which type of electromagnetic wave has a lower frequency than microwaves?... () (ii) What do all types of electromagnetic wave transfer from one place to another?... () (b) The picture shows a tennis coach using a speed gun to measure how fast the player serves the ball. (i) The microwaves transmitted by the speed gun have a frequency of Hz and travel through the air at m/s. Use the equation in the box to calculate the wavelength of the microwaves emitted from the speed gun. wave speed = frequency wavelength Show clearly how you work out your answer

28 ... (ii) Wavelength =... m (2) Some of the microwaves transmitted by the speed gun are absorbed by the ball. What effect will the absorbed microwaves have on the ball? () (iii) Some of the microwaves transmitted by the speed gun are reflected from the moving ball back towards the speed gun. Describe how the wavelength and frequency of the microwaves change as they are reflected from the moving ball (2) (Total 7 marks) (a) The wavelengths of four different types of electromagnetic wave, including visible light waves, are given in the table. Type of wave Visible light A B C Wavelength mm. km 00 mm 0.8 mm Which of the waves, A, B or C, is an infra red wave?... () (b) A TV station broadcasts at khz. The waves travel through the air at m/s. Use the equation in the box to calculate the wavelength of the waves broadcast by this station. wave speed = frequency wavelength Show clearly how you work out your answer. 27

29 (c) Wavelength =... m(2) What happens when a metal aerial absorbs radio waves? (2) (d) Stars emit all types of electromagnetic waves. Telescopes that monitor X-rays are mounted on satellites in space. Why would an X-ray telescope based on Earth not be able to detect X-rays emitted from distant stars? () (Total 6 marks) 28

30 Mark scheme M. (a) gamma rays above x-rays for mark M3. (i) X-rays or gamma rays for mark (b) upper radio wave boundary correct (0 - m) (± mm) (c) visible radiation/light for mark (ii) passes through flesh; stopped by bone/absorbed for mark each 2 [3] (d) (e) (f) within the middle third of a wavelength band in the correct wavelength range ( m) each for mark ultraviolet between *visible radiation and X-rays for mark microwaves above *radio waves and below *infra red (*not necessarily immediately) for mark between 0 8 Hz Hz and nearer to 0 8 Hz than to 0 7 Hz gains mark M2. (a) radio 500 ultra violet visible X-rays 0 4 [7] M5. (a) (i) to compare mobile phone usage between the two groups (ii) (b) (i) ethical (ii) (iii) enough data to indicate relationships or reduce effect of anomalous data research may be biased (in favour of companies) negative effects on health may not get published accept negative effects on health may be played down it allows people to easily identify lower risk phones (b) 0 0 Hz 0 0 HzOK for 4 marks else 0 0 for 3 marks else /0.03 for 2 marks and this allows people to make a more informed choice accept and this allows a comparison to be made M6 (i) X-rays infra red (rays) radio (waves) all three in correct order allow mark for correct 2 [7] else v = frequency wavelength or = 0.03f any answer with unit Hz scores, 2 or 3 (ii) to kill cancer cells for mark 4 [8] (iii) energy [4] 29

31 M7. (a) (i) total internal reflection shown (2 8 reflections) M8. Quality of written communication award for a sensible sequence of two points (ii) accept easier to get into patient or more flexible accept more detailed or better image accept if some fibres broke system would not fail do not accept to pass more light - neutral (iii) any one of the following: do not accept any further endoscopy uses angles look correct (by eye) (2 5 reflections) can be bent more (without loss of light) (telephone) communications (carry (laser) light) for surgery or operations torches guides in cars table lamps or ornamental lights do not accept telephone wires carry TV signals carry computer data or information cable TV or cable telephone do not accept TV or telephone or computers without qualification do not accept bomb disposal unless qualified accept to stimulate children with learning difficulties (b) (both) longitudinal accept both have compressions or rarefactions accept both have high or low pressure regions accept both transfer energy do not accept 'need a medium' X-rays do not go through lead accept lead protects them from the X-rays accept not exposed to X-rays lead stops / reduces risk of X-rays harming / damaging / killing (persons) cells accept X-rays (may) cause cancer accept organs for cell do not accept references to electric shock do not accept stops bones of people showing on X-ray answers involving the horse wearing an apron are incorrect references to gamma rays are incorrect M9. (a) X-rays are ionising or X-rays kill / damage cells accept cause cancer (b) [3] any stray X-rays are absorbed by screen which reduces the radiation dose to the radiographer medical records / X-ray records of people with cancer (c) a CT scan gives a 3D image (c) or liquids have a greater density therefore the image can be observed from different directions [7] molecular spacing in gases is greater (d) (bat) transmits or emits ultrasound or pulses or signals or sound or waves allow one mark if response is in terms of distance and time allow mark for echo location picks up reflected ultrasound or signals or waves or sound or echo [8] M0. (a) (i) radio(waves) (ii) energy correct answer only (b) (i) (m) allow mark for correct transformation and substitution (ii) make it hot(ter) do not accept cook it accept (air) particles inside ball will move faster accept water in the ball gets hotter 2 (iii) wavelength decreases ignore reference to speed frequency increases [7] 30

32 M. (a) C or 0.8 mm (b) 0.6 m allow mark for correct transformation and substitution allow mark for changing frequency to Hz answer 600 gains mark (c) creates an alternating current accept ac for alternating current accept alternating voltage 2 accept signal for radio wave with the same frequency as the radio wave or it gets hotter (d) X-rays cannot penetrate the atmosphere accept atmosphere stops X-rays do not accept atmosphere in the way before reaching Earth ignore explanations or X-rays are absorbed (by the atmosphere) [6] Communicate - stay in touch Answers a) Short wavelength Long wavelength gamma rays X-rays ultraviolet visible infra-red microwaves radio waves 0-4 m 0-0 m 0-8 m 0-6 m 0-5 m 0-2 m 0 3 m b i Transverse, carry energy, diffract, reflect and refract. ii Gamma rays. iii frequency = wave speed / wavelength v frequency of radio waves = = 3 05 Hz frequency of microwaves = 3 x 0 0 Hz students may use ratios to show this. 3

33 2a e.g. b Above 300 MHz. c Radio waves reflect from the ionosphere then reflect off the Earth and may take several hops (reflections) to travel to the other side of the Earth. d The radio wave is reflected by the ionosphere. The ionosphere changes its ability to reflect. It may move up or down or disappear for a time. e In absorption, the energy of the wave is transferred to an object usually causing the object to heat up. Reflection is the bouncing back of the wave. f Mobile phones, Bluetooth, communicating with computers etc. Discussion Possible answers include: Skin cancer, death of some species of animals caused by more ultraviolet radiation reaching the Earth s surface. Greenhouse warming is caused by gases such as carbon dioxide which trap heat, i.e. do not allow infrared radiation to escape from the Earth. Loss of the ozone layer allows more ultraviolet radiation to reach the Earth because it is, at present, absorbed by the ozone layer. 32