2The Electromagnetic Spectrum Each type of radiation shown in the electromagnetic spectrum has a different wavelength and a different frequency:Gamma raysX-raysUltra violetVisible lightInfra redMicrowavesRadio/TVγHigh frequency, _____ wavelengthLow frequency, _____ (high) wavelengthAll waves travel at m/s in a vacuum
3Radio waves and microwaves? Sending signals by light, electricity and radio and microwaves all have various advantages and disadvantages.Light signals?Electrical signals?Radio waves and microwaves?Can be easily sent with nothing more sophisticated than a torch, but the signal needs to be coded and is not secure.(eg house telephone)Need equipment and wires linking the sender and receiver of the signal. Wires can be cut or damaged. Signal needs to be amplified at regular intervals because of loss of energy in form of heat due to the electric current.(eg satellite, mobile, radio)These can travel very large distances and through the atmosphere – and even across space!
4Comparing infra-red and microwave cookery HigherInfra-red cooked food is usually browned, Microwave cooked food is not.This is because of the way the energy is transferred.Infra-red:Energy is absorbed by the particles on the surface of the food.This increases the kinetic energy of the particles. The energy is then transferred to the rest of the food by conduction.Microwaves:the water molecules in the outer layers vibrate more and their kinetic energy increases.The energy is then transferred to the rest of the food by convection and conductionWhich cooks quickest?
5Infrared control Remote control garage doors Cordless mice GrillingInfrared controlBar code readersTV & video controllersSatellite picturesRemote control garage doorsCordless miceSecurity alarmsInfrared photographs
6Electromagnetic Spectrum - To do 1. Which parts of the spectrum can be used in communication?2. What are the concerns about using mobile phones?Which two waves in the spectrum can be used to cook food. Describe the differences between the two methodsRadio, microwaves and lightIf microwaves are absorbed by water molecules in living tissue, cells may be burned/killed. Potential dangers are prolonged exposure but there is no conclusive evidenceMicrowaves and Infrared . Microwaves heat water molecules in food and IR heats the surface of the food
7Reflection, Refraction and Diffraction all electromagnetic waves can be reflected, refracted and diffracted.Reflection:The wave changes direction at a boundary. It returns in the direction it originated.Refraction:A change in direction due to the speed of the wave. (caused by entering a different medium; e.g. light from air into water)Diffraction:Bending of waves caused by obstacles. The degree and type of diffraction depends on the obstaclecopy
8Angle of incidence = Angle of reflection NormalIncident rayReflected rayAngle of incidenceAngle of reflectionMirror13/04/2017
9Refraction through a glass block: Wave slows down and bends towards the normal due to entering a more dense mediumWave slows down but is not bent, due to entering along the normalWave speeds up and bends away from the normal due to entering a less dense medium13/04/2017
11Diffraction – Higher only More diffraction if the size of the gap is similar to the wavelengthMore diffraction if wavelength is increased (or frequency decreased)
12Diffraction depends on frequency… A high frequency (short wavelength)microwaves -wave doesn’t get diffracted much – the house won’t be able to receive it…
13Diffraction depends on frequency… A low frequency (long wavelength) radio waves wave will get diffracted more, so the house can receive it…
14Sending information - Finding the Critical Angle… 1) Ray gets refracted2) Ray still gets refracted4) Ray gets internally reflected3) Ray still gets refracted (just!)THE CRITICAL ANGLE
15Uses of Total Internal Reflection Optical fibres: Use total internal reflection to send informationUses – communication systems, endoscope, binoculars
16Light Amplification by Stimulated Emission of Radiation White light from a bulb is made up of many different colours. Each is of a different frequency and is out of PHASE.The light from a LASER is at just one frequency and is in phase. This makes it very much brighter and able to travel further that ordinary white light.Lasers produce narrow, intense beams of monochromatic light
17Higher - Compact DiscsPlastic disc with a billions of pits on the bottom shiny surface (coated with metal film)The pits represent a digital signalThe signal is read by a laserThe shiny metal film reflectsthe laser light
18Questions Name 2 uses of lasers. Why is it dangerous to look at a laser beam?What is morse code and why is it important?1. communication, dental treatment, surgery, light shows, bar code readers2. Narrow intense beam of light capable of cutting, burning or vaporising materials3. Digital signal - Series of dots and dashes representing letters of the alphabet. Used to send messages
196 mark questionThe quality of written communication will be assessed in your answer to this question.Describe how light signals can travel through optical fibres and why they are important13/04/2017
20Level 3Answer correctly applies knowledge of how light signals bouncing waves off the sides of narrow core, they enter the fibre so it hits the boundary between the core and the outer cladding at an angle greater than the critical angle, causing total internal reflection. Pulse of light enters at one end and is reflected again and again until it emerges at the other end .Uses – telephone conversations and computer data All information in answer is relevant, clear, organised and presented in a structured and coherent format. Specialist terms are used appropriately. Few, if any, errors in grammar, punctuation and spelling. (5–6 marks)Level 2Answer applies knowledge of how light signals can pass through an optical fibre and why they are important. For the most part the information is relevant and presented in a structured and coherent format. Specialist terms are used for the most part appropriately. There are occasional errors in grammar, punctuation and spelling. (3–4 marks)Level 1An incomplete answer, states that light signals are totally internally reflected and mentions a use. Answer may be simplistic. There may be limited use of specialist terms. Errors of grammar, punctuation and spelling prevent communication of the science. (1–2 marks)Level 0Insufficient or irrelevant science. Answer not worthy of credit. (0 marks)13/04/2017
21Analogue vs. DigitalAnalogue signals (like talking or music) continually vary in amplitude and/or frequency+-1Digital signals, however, are either off or on, and the information is sent in a series of pulsesThere are two main advantages of digital:More information can be sent down the same cableBetter quality, because a digital signal can be amplified without amplifying the extra noise:
22Transmitting information – Higher As we said before, different types of electromagnetic radiation can be used to send different types of information, e.g. an optical fibre:Optical fibres have two main advantages: they can send more information compared to electrical cables of the same diameter and with less signal weakening.Another example is radio waves:IonosphereThe short wave radio (TV and FM) and medium radio waves are transmitted by being reflected off the ionosphere (an electrically charged layer in the Earth’s atmosphere).Long wave radio waves diffract (bend) around the Earths surface
23Uses of radio wavesterrestrial frequency Ultra waves long high Very curvature distant ionosphere Longer Earth transmitRadio waves are used to __________ radio and television programmes between different points on the __________’s surface. __________ wavelength radio waves are reflected from an electrically charged layer in the Earth’s upper atmosphere, which is called the __________. This enables them to be sent between __________ points despite the __________ of the Earth’s surface. __________ __________ frequency (VHF) radio waves allow higher quality audio transmission than __________ waves or medium __________ __________ high __________ (UHF) radio waves are used for television and by the police.
24abcabcabcabcabcabcabcabc Multiplexing:This allows many different signals to be transmitted simultaneously, with less interferenceEach digital signal is divided into segments of very short duration.A combined signal takes each segment in turn and transmits it. A multiplexer combines the individual signals to be sent and a demultiplexer separates them at the receiving end of the transmission.higherdemultiplexerSignal AaaaaaaaaaaaaaaaaaSignal BbbbbbbbbbbbbbbbSignal CccccccccccccccccmultiplexerSignal AaaaaaaaaaaaaaaaaaSignal BbbbbbbbbbbbbbbbSignal CccccccccccccccccTransmitted asabcabcabcabcabcabcabcabcUsed in telecommunications and computer networks
25Multiplexing and the digital switchover Due to the large amount of data that can be sent due to multiplexing, the switch from analogue to digital has been made possible.The main benefits of digital television and radio are:Improved signal quality (sound and image)Improved choice of programmesInteraction with programmes (e. g. red buttonProgramme guides
266 mark question - HigherThe quality of written communication will be assessed in your answer to this question.Lisa lives in a house in the valley. He can listen to long-wave and medium wave stations on his radio. He can’ t get any signal on his mobile phone and VHF (very high frequency used for FM) reception is very poor. Explain these differences13/04/2017
2713/04/2017Level 3Answer correctly applies knowledge of how long and medium wave signals diffracted around the obstacle to his house; some diffraction with VHF; however microwaves have an even shorter wavelength so do not diffract as much. Microwave transmitter needs to be in the line of sight. All information in answer is relevant, clear, organised and presented in a structured and coherent format. Specialist terms are used appropriately. Few, if any, errors in grammar, punctuation and spelling. (5–6 marks)Level 2Answer applies knowledge of how microwaves do not diffract as much as radio waves therefore it can’t be received at the house behind the hill, and how the transmitter needs to be in the line of sight. For the most part the information is relevant and presented in a structured and coherent format. Specialist terms are used for the most part appropriately. There are occasional errors in grammar, punctuation and spelling. (3–4 marks)Level 1An incomplete answer, states that radio waves diffract more than microwaves . Answer may be simplistic. There may be limited use of specialist terms. Errors of grammar, punctuation and spelling prevent communication of the science. (1–2 marks)Level 0Insufficient or irrelevant science. Answer not worthy of credit. (0 marks)
28Questions What type of EM wave is used in satellite communication? Give 2 disadvantages of the use of microwaves in mobile phones3. What are digital and analogue signals. What is the advantage of sending information digitally?Give 3 uses of IR.5. Why is it said that texting is a safer way to communicate than making a call from a mobile phone?
29AnswersMicrowavesDon’t diffract as much due to short wavelength so transmitters need to be in line of sight, interference between signals (affected by weather)Digital – on/off, analogue can take any value. Advantage – better quality, send several signals at the same time (multiplexing)Security systems, remote controls, mobile phones and computers (only short distances though and must point directly)There has been reports that mobile phones may be dangerous if absorbed by water molecules in living tissue, cells may be burned. However there is no conclusive evidence, if there was surely mobile phones would be designed to give out less microwaves and there would be a legal age limit for use or use for emergency calls only
30TermMeaningA radio wave1 distance occupied by one complete cycle of a waveB refraction2 the shortest wavelength radio waves in the electromagnetic spectrumC frequency3 the complete range of observed frequencies of electromagnetic wavesD microwaves4 the change in direction of a wave when it passes from one medium to another of different densityE aerial5 poor radio reception caused by overlapping wavesF ionosphere6 part of the electromagnetic spectrum used mainly for communicationG interference7 a layer of the upper atmosphere that reflects some radio wavesH wavelength8 the number of complete waves passing a point in 1 secondI electromagnetic spectrumeffect of two signals from the same source which havetravelled different distances to reach a television aerialJ ghosting10 device for receiving or transmitting radio signals
31Some definitions…Transverse waves are when the displacement is at right angles to the direction of the wave…Longitudinal waves are when the displacement is parallel to the direction of the wave…
32Some definitions… 1) Amplitude – this is “how high” the wave is: 2) Wavelength () – this is the distance between two corresponding points on the wave and is measured in metres:3) Frequency – this is how many waves pass by every second and is measured in Hertz (Hz)
33Wave speed (v) = frequency (f) x wavelength () The Wave EquationThe wave equation relates the speed of the wave to its frequency and wavelength:Wave speed (v) = frequency (f) x wavelength ()in m/s in Hz in mVf
34Some example wave equation questions A water wave travels through a pond with a speed of 1m/s and a frequency of 5Hz. How far apart are the waves?The speed of sound is 330m/s (in air). When Ricky hears this sound his ear vibrates 660 times a second. What was the wavelength of the sound?Purple light has a wavelength of around 6x10-7m. If its frequency is 5x1014 Hz what is the speed of light?Red light travels at the same speed. Work out its frequency if its wavelength is about 4x10-7m.
35The Structure of the Earth A thin crust km thickA mantle – has the properties of a solid but it can also flowA core – made of molten nickel and iron. Outer part is liquid and inner part is solidHow do we know this? These facts have all been discovered by examining seismic waves (earthquakes)
36Seismic waves P waves: S waves: Earthquakes travel as waves through the Earth – we call them SEISMIC WAVES. There are two types:P waves:They are longitudinal so they cause the ground to move up and downThey can pass through solids and liquidsThey go faster through more dense materialS waves:They are transverse so they cause the ground to move from right to leftThey ONLY pass through solidsThey are slower than P wavesThey go faster through more dense material
37Waves through the Earth - Questions 1. How do we know the structure of the Earth?2. Describe two differences between p and s waves3. Name one advantage and disadvantage of seismometer.1. How Seismic waves, such as P and S waves travel through the Earth2. S waves can only travel through solids and are slower than p waves. P waves can travel through solids and liquids. S waves are transverse and P waves are longitudinal3. Advantage e.g. seismometers detect p waves before more damaging s waves arrive so people can get to a safe place. Disadvantage – they record information after an earthquake has happened so may not give much warning
38Human effect on the Earth Use of CFC’s in aerosols has meant that the ozone layer has become damaged. This means that more of the Sun’s harmful U.V. is reaching usBurning fossil fuels is producing carbon dioxide (a greenhouse gas). This is trapping in the heat and contributing to global warming
39Avoiding SunburnSun index gives information about the strength of the sun and how long you can stay in the sun without burning if you are not wearing sunscreen.Sun protection factor (SPF) is an indication of how much longer you can stay in the Sun when using sunscreen; SPF 10 means 10 times longer, etc.SPF safe time given by sun index = time you can stay in the Sun with that SPF sunscreen.
40Quick questionWhat is the maximum amount of time you could spend in the sun if the sun index is 8 and you put on sun cream with a SPF factor of 8?Safe time = SPF no. X time given insun index8 x min= 160 min – 240 min
41QuestionsWhat can happen when a person is exposed to too much UV radiation?Why are people with darker skin less likely to suffer from skin cancer?What does a SPF 15 mean?Why are scientists concerned about the thinning of the ozone layer?UV radiation can damage the DNA in your cells, which may lead to skin cancer, it can cause eye problems such as cataracts, as well as premature skin aging2. The skin absorbs more of the UV so less reaches the cells that may become cancerous3. You can stay out in the sun 15 times as long4. Ozone layer has got thinner due to the overuse of CFCs, this allows more UV rays to reach us at the surface of the Earth
42Plenary - To DoProduce a summary sheet / mind map for the P1 – Energy for the Home topic