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and its uses Radar and its uses

Introduction Development of radar 960 MHz – 1215 MHz Aeronautical Radionavigation: Distance Measuring; Transmitted Secondary Surveillance Radar In the years 1933–1939 researchers in a number radar pulse 2700 MHz – 2900 MHz Radar and Navigation Systems; Meteorological The word radar is an for Detection And of countries developed radar systems, mainly for Reflected radar; Maritime Radionavigation Ranging. Common applications include air and marine defence purposes. These systems used short pulse monitoring, , geology, astronomy and duration radio pulses and displayed the returning 7900 MHz – 8025 MHz Meteorological Satellite; Earth exploration satellite on a screen. service; Industrial Level Probing Radar detection of motor cars. time delay 8750 MHz – 8850 MHz Airborne Radio signals travel at almost 300,000 kilometres 8 −1 2.4 GHz – 2.5 GHz Mobile phones In a typical radar system a radio is directed per second (3×10 m s ). If the echo returns in 0.1 Early radar display ComReg is the statutory body responsible for the regulation of towards the object and the reflected signal is detected; using milliseconds (i.e. 1×10 −4 s) then the radio signal 23.6 GHz – 24 GHz the electronic sector (telecommunications, 8 −1 −4 the time for the ‘echo’ to return, the distance to the object can travelled a distance of (3×10 m s )×(1×10 s) = 79 GHz – 81 GHz Radio Astronomy radiocommunications and transmission) and the be calculated. 30,000 m. Since this is the time for the signal to postal sector. Its remit covers all kinds of transmission travel to the object and back again the distance to networks including: the object is half that value, i.e. 15,000 m or 15 km. Note that particular applications may be allocated several bands in the RF time delay spectrum and one band may be available for different applications. • Traditional telephone wire Water and electromagnetic waves Note that in a all electromagnetic waves travel at the save speed; in air at atmospheric Line representing The band 2700 MHz to 2900 MHz is in use worldwide as the primary air traffic • and radio When a stone is thrown into water it produces oscillations, i.e. the water rotating radar pressure the speed is about 99.97% of the speed ‘beam’ control radar band. In Ireland there are 4 covering the country; in the UK, moves down and then returns towards its original position. However, as it • Radiocommunications including fixed wireless in a vacuum. (In other media the speed may be due to the larger land mass and a far greater number of airports, there are about returns it gathers speed and overshoots the equilibrium level. The considerably less.) Rotating radar display 40 radars and in the USA the national air traffic network uses 159 radars. • Mobile operators providing voice and data services oscillations continue for some time and the disturbance is propagated outwards as circles of ever increasing diameter. As they travel outwards from • Satellite services the source the waves carry energy. The waves can be reflected by structures The Using different or boundaries; they can be refracted if they are slowed down (for example ComReg enables competition in the communications sector by facilitating market entry for networks and services and by by going into shallower water); they can be diffracted around objects such The choice of to use for radar depends on the application. The wide range of different kinds of electromagnetic radiation is referred to regulating access to networks so as to ensure that consumers, as rocks or piers. Shorter wavelengths are reflected by smaller objects and so give higher as the electromagnetic spectrum. It includes X-rays, (UV), visible both business and residential, have choice in the services , (IR), and radio waves. They differ in their resolution. However they are also absorbed more easily by the target and so which they wish to use. In a rapidly evolving sector, both In the early 1800s light was shown to have these same properties and so it produce little ‘echo’. For example, 7.5–15 cm (2–4 GHz) radar is used to was considered to be some kind of . In 1832 Michael Faraday had frequency and consequently in their wavelength. The higher the frequency, in technological and commercial terms, ComReg provides the shorter the wavelength. track the movement of clouds and rain at distances up to 150 km and heights the framework for the introduction of new services such as already come to the conclusion that light was some kind of electromagnetic of up to 15 km above the ground; however the receiving dish may be 8 m in wave although it took him over ten years to get the evidence he had been next generation mobile to support smartphones and diameter and so such radar equipment is not normally mobile. Shorter similar applications. looking for. wavelengths (3 cm, 10 GHz) are suitable for tracking local movement There is a simple relationship between the speed, wavelength and at airports or local conditions. Encouraging innovation is also a key role for ComReg. This We now know that light (and all the other kinds of electromagnetic wave) can frequency of waves: speed = frequency × wavelength, or using the usual be described as a magnetic oscillation and an electric oscillation Portable systems for measuring the speed of cars typically use 1.5 cm (20 covers both regulatory innovations, such as implementation of symbols: v = f λ. (λ is the Greek lower case letter ‘L’, for wavelength) market reviews under the new European regulatory framework, perpendicular to one GHz) waves. another. If all the waves Example: If a radio station broadcasts on 90 MHz, what is the and technical innovations. On the side the role involves development of strategies for management and use from a source have the wavelength of the signal? of the radio spectrum, new initiatives in the wireless licensing electric oscillation in, for Doppler Radar Rearranging the relationship v = f λ we see that λ = v ÷ f. area, and the promotion of Ireland as a test bed for innovative example, a vertical uses of spectrum (See Test & Trial Ireland at www.testandtrial. direction then the wave is Substituting the known values we get: A note emitted by an approaching sound source appears to have a higher (frequency); as the source moves away the pitch of the note is lowered. ie). ComReg publishes the following websites, offering a wide said to be vertically λ = (3×10 8 m s −1) ÷ (90 ×10 6 Hz) pitch A common example of this effect is the change in pitch of an ambulance range of information and advice to users. polarised. (Satellite TV Magnetic component 2 −1 −1 λ = (3×10 m s ) ÷ (90 s ) siren as it passes by. It is called the after Christian Andreas transmissions are Advice for communications consumers generally polarised either Electric component λ = (30 m) ÷ (9) Doppler (1803 – 1853) who first analysed it and used it to explain the colour www.askcomreg.ie vertically or horizontally.) λ = 3.3 m change in certain binary stars. Interactive guide on phone and broadband pricing When an electromagnetic wave bounces off a stationary target the reflected www.callcosts.ie wave has the same frequency as the incident wave. However if the target is Development of radio Radar frequency bands approaching then the frequency of the reflected wave will be increased by Information on Premium Rate services www.phonesmart.ie the following amount: f ×2v/c, where v is the speed of the target (such as a In 1888 the German physicist Heinrich demonstrated the propagation The part of the electromagnetic (EM) spectrum that is used for motor car), c is the speed of electromagnetic waves (3×10 8 m s −1 ) and f is of radio waves as had been predicted by James Clerk Maxwell in 1871. He Statistical information on the Irish electronic communications market telecommunications is called the radio frequency spectrum. This is the part the frequency of the source. (Note: The expression f×2v/c applies for www.comstat.ie showed that radio waves travelled at the and were of the same of the EM spectrum with wavelengths greater than 1 mm, or in other words non-relativistic , i.e. when v is much less than the speed of light.) nature as light, but with longer wavelengths. Over the following decade with frequencies less than 300 GHz; this includes microwaves (300 MHz to Find out more about the work of ComReg at −1 many experimentalists tried to devise systems using these 300 GHz and wavelengths from 1 m down to 1 mm). For a car approaching a 20 GHz radar source at 20 m s (i.e. 72 km/h) the www.comreg.ie ‘radio’ waves. In 1897 the Italian inventor Guglielmo Marconi demonstrated a reflected frequency is 20.000002666 GHz, that is an increase of 2666 Hz. ‘wireless telegraph’ system. (At that time wire-based telegraph had then The radio frequency (RF) spectrum is divided into hundreds of bands that This change in frequency is measured by the receiving equipment and been in use for over 50 years.). Within a few years Marconi’s wireless system are used for different purposes, such as broadcast TV and radio, mobile processed to display the speed of the car. was being used for long distance communication. phones, radar, meteorology and satellite communications. There are detailed national and international specifications for the use of the RF spectrum. In Although radar-based traffic monitoring is being replaced by more compact In 1935, Robert Watson- and his colleague Arnold Wilkins demonstrated Ireland these are set by ComReg and the current specification (or ‘Radio systems, radar is finding new applications in sports such as tennis the detection of BBC radio signals reflected off an aeroplane many Frequency Plan’) may be found on the ComReg website under ‘Publications’. where it is used to measure the maximum speed of the ball, i.e. the player’s Find this and other lessons on www.sta.ie kilometres away ─ the operating principle of radar. In 1933 German naval serve speed. However the most important uses of radar remain air traffic scientists had detected echoes of radio signals from ships. A small number of bands are shown in the following table. control, navigation and weather monitoring. Radar and its uses Radar and its uses

Introduction Development of radar 960 MHz – 1215 MHz Aeronautical Radionavigation: Distance Measuring; Transmitted Secondary Surveillance Radar In the years 1933–1939 researchers in a number radar pulse 2700 MHz – 2900 MHz Radar and Navigation Systems; Meteorological The word radar is an acronym for Radio Detection And of countries developed radar systems, mainly for Reflected radar; Maritime Radionavigation Ranging. Common applications include air and marine traffic defence purposes. These systems used short pulse monitoring, meteorology, geology, astronomy and speed duration radio pulses and displayed the returning 7900 MHz – 8025 MHz Meteorological Satellite; Earth exploration satellite signals on a screen. service; Industrial Level Probing Radar detection of motor cars. time delay 8750 MHz – 8850 MHz Airborne Doppler Radar Radio signals travel at almost 300,000 kilometres 8 −1 2.4 GHz – 2.5 GHz Mobile phones In a typical radar system a radio frequency signal is directed per second (3×10 m s ). If the echo returns in 0.1 Early radar display ComReg is the statutory body responsible for the regulation of towards the object and the reflected signal is detected; using milliseconds (i.e. 1×10 −4 s) then the radio signal 23.6 GHz – 24 GHz Radio Astronomy the electronic communications sector (telecommunications, 8 −1 −4 the time for the ‘echo’ to return, the distance to the object can travelled a distance of (3×10 m s )×(1×10 s) = 79 GHz – 81 GHz Radio Astronomy radiocommunications and broadcasting transmission) and the be calculated. 30,000 m. Since this is the time for the signal to postal sector. Its remit covers all kinds of transmission travel to the object and back again the distance to networks including: the object is half that value, i.e. 15,000 m or 15 km. Note that particular applications may be allocated several bands in the RF time delay spectrum and one band may be available for different applications. • Traditional telephone wire Water waves and electromagnetic waves Note that in a vacuum all electromagnetic waves travel at the save speed; in air at atmospheric Line representing The band 2700 MHz to 2900 MHz is in use worldwide as the primary air traffic • Television and radio frequencies When a stone is thrown into water it produces oscillations, i.e. the water rotating radar pressure the speed is about 99.97% of the speed ‘beam’ control radar band. In Ireland there are 4 radars covering the country; in the UK, moves down and then returns towards its original position. However, as it • Radiocommunications including fixed wireless in a vacuum. (In other media the speed may be due to the larger land mass and a far greater number of airports, there are about returns it gathers speed and overshoots the equilibrium level. The considerably less.) Rotating radar display 40 radars and in the USA the national air traffic network uses 159 radars. • Mobile operators providing voice and data services oscillations continue for some time and the disturbance is propagated outwards as circles of ever increasing diameter. As they travel outwards from • Satellite services the source the waves carry energy. The waves can be reflected by structures The Electromagnetic Spectrum Using different wavelengths or boundaries; they can be refracted if they are slowed down (for example ComReg enables competition in the communications sector by facilitating market entry for networks and services and by by going into shallower water); they can be diffracted around objects such The choice of wavelength to use for radar depends on the application. The wide range of different kinds of electromagnetic radiation is referred to regulating access to networks so as to ensure that consumers, as rocks or piers. Shorter wavelengths are reflected by smaller objects and so give higher as the electromagnetic spectrum. It includes X-rays, ultraviolet (UV), visible both business and residential, have choice in the services light, infrared (IR), microwaves and radio waves. They differ in their resolution. However they are also absorbed more easily by the target and so which they wish to use. In a rapidly evolving sector, both In the early 1800s light was shown to have these same properties and so it produce little ‘echo’. For example, 7.5–15 cm (2–4 GHz) radar is used to was considered to be some kind of wave. In 1832 Michael Faraday had frequency and consequently in their wavelength. The higher the frequency, in technological and commercial terms, ComReg provides the shorter the wavelength. track the movement of clouds and rain at distances up to 150 km and heights the framework for the introduction of new services such as already come to the conclusion that light was some kind of electromagnetic of up to 15 km above the ground; however the receiving dish may be 8 m in wave although it took him over ten years to get the evidence he had been next generation mobile to support smartphones and diameter and so such radar equipment is not normally mobile. Shorter similar applications. looking for. wavelengths (3 cm, 10 GHz) are suitable for tracking local aircraft movement There is a simple relationship between the speed, wavelength and at airports or local weather conditions. Encouraging innovation is also a key role for ComReg. This We now know that light (and all the other kinds of electromagnetic wave) can frequency of waves: speed = frequency × wavelength, or using the usual be described as a magnetic oscillation and an electric oscillation Portable systems for measuring the speed of cars typically use 1.5 cm (20 covers both regulatory innovations, such as implementation of symbols: v = f λ. (λ is the Greek lower case letter ‘L’, for wavelength) market reviews under the new European regulatory framework, perpendicular to one GHz) waves. another. If all the waves Example: If a radio station broadcasts on 90 MHz, what is the and technical innovations. On the radio spectrum side the role involves development of strategies for management and use from a source have the wavelength of the signal? of the radio spectrum, new initiatives in the wireless licensing electric oscillation in, for Doppler Radar Rearranging the relationship v = f λ we see that λ = v ÷ f. area, and the promotion of Ireland as a test bed for innovative example, a vertical uses of spectrum (See Test & Trial Ireland at www.testandtrial. direction then the wave is Substituting the known values we get: A note emitted by an approaching sound source appears to have a higher (frequency); as the source moves away the pitch of the note is lowered. ie). ComReg publishes the following websites, offering a wide said to be vertically λ = (3×10 8 m s −1) ÷ (90 ×10 6 Hz) pitch A common example of this effect is the change in pitch of an ambulance range of information and advice to users. polarised. (Satellite TV Magnetic component 2 −1 −1 λ = (3×10 m s ) ÷ (90 s ) siren as it passes by. It is called the Doppler effect after Christian Andreas transmissions are Advice for communications consumers generally polarised either Electric component λ = (30 m) ÷ (9) Doppler (1803 – 1853) who first analysed it and used it to explain the colour www.askcomreg.ie vertically or horizontally.) λ = 3.3 m change in certain binary stars. Interactive guide on phone and broadband pricing When an electromagnetic wave bounces off a stationary target the reflected www.callcosts.ie wave has the same frequency as the incident wave. However if the target is Development of radio Radar frequency bands approaching then the frequency of the reflected wave will be increased by Information on Premium Rate services www.phonesmart.ie the following amount: f ×2v/c, where v is the speed of the target (such as a In 1888 the German physicist demonstrated the propagation The part of the electromagnetic (EM) spectrum that is used for motor car), c is the speed of electromagnetic waves (3×10 8 m s −1 ) and f is of radio waves as had been predicted by James Clerk Maxwell in 1871. He Statistical information on the Irish electronic communications market telecommunications is called the radio frequency spectrum. This is the part the frequency of the source. (Note: The expression f×2v/c applies for www.comstat.ie showed that radio waves travelled at the speed of light and were of the same of the EM spectrum with wavelengths greater than 1 mm, or in other words non-relativistic speeds, i.e. when v is much less than the speed of light.) nature as light, but with longer wavelengths. Over the following decade with frequencies less than 300 GHz; this includes microwaves (300 MHz to Find out more about the work of ComReg at −1 many experimentalists tried to devise communication systems using these 300 GHz and wavelengths from 1 m down to 1 mm). For a car approaching a 20 GHz radar source at 20 m s (i.e. 72 km/h) the www.comreg.ie ‘radio’ waves. In 1897 the Italian inventor Guglielmo Marconi demonstrated a reflected frequency is 20.000002666 GHz, that is an increase of 2666 Hz. ‘wireless telegraph’ system. (At that time wire-based telegraph had then The radio frequency (RF) spectrum is divided into hundreds of bands that This change in frequency is measured by the receiving equipment and been in use for over 50 years.). Within a few years Marconi’s wireless system are used for different purposes, such as broadcast TV and radio, mobile processed to display the speed of the car. was being used for long distance communication. phones, radar, meteorology and satellite communications. There are detailed national and international specifications for the use of the RF spectrum. In Although radar-based traffic monitoring is being replaced by more compact In 1935, Robert Watson-Watt and his colleague Arnold Wilkins demonstrated Ireland these are set by ComReg and the current specification (or ‘Radio laser systems, radar is finding new applications in sports such as tennis the detection of BBC radio signals reflected off an aeroplane many Frequency Plan’) may be found on the ComReg website under ‘Publications’. where it is used to measure the maximum speed of the ball, i.e. the player’s Find this and other lessons on www.sta.ie kilometres away ─ the operating principle of radar. In 1933 German naval serve speed. However the most important uses of radar remain air traffic scientists had detected echoes of radio signals from ships. A small number of bands are shown in the following table. control, navigation and weather monitoring. RadarRadar and and its its uses uses

Radar and its uses

SyllabusSyllabus references references StudentStudent Activities Activities ExaminationExamination Questions Questions DidDid You You Know? Know?

TheThe main main syllabus syllabus references references for for the the lesson lesson are: are: ByBy 1905 1905 the the photoelectric photoelectric effect effect had had been been puzzling puzzling scientists scientists for for nearly nearly LeavingLeaving Certificate Certificate Physics Physics (HL) (HL) 2010, 2010, Q. Q.7 7 • • If Ifa apiece piece of of metal metal is isheated heated and and becomes becomes ‘red ‘red hot’ hot’ it itemits emits some some 2020 years. years. In In Einstein’s Einstein’s explanation, explanation, published published in in 1905 1905 when when he he was was just just visiblevisible red red light light but but considerable considerable more more invisible invisible infrared infrared radiation. radiation. LeavingLeaving Certificate Certificate Physics Physics TheThe Doppler Doppler effect effect applies applies to to all all types types of of waves waves and and is isnamed named after after 2626 years years of of age, age, light light is isconsidered considered to to be be composed composed of of particles particles which which InIn fact fact it itemits emits radiation radiation with with a awide wide range range of of wavelengths wavelengths with with a a ChristianChristian Johann Johann Doppler, Doppler, an an Austrian Austrian scientist scientist who who explained explained this this hehe called called ‘photons’. ‘photons’. The The energy energy carried carried by by a aphoton photon depends depends on on its its peakpeak in in the the IR IR region. region. If Ifit itis isheated heated further, further, say say to to 1500 1500 °C, °C, the the • • WaveWave phenomena: phenomena: , reflection, , refraction, , diffraction, interference, interference, phenomenonphenomenon in in 1842. 1842. polarisation.polarisation. frequencyfrequency ─ ─which which is isa awave wave characteristic characteristic ─ ─and and is isgiven given by by the the peakpeak radiation radiation moves moves into into the the visible visible part part of of the the spectrum spectrum and and the the • • SimpleSimple demonstrations demonstrations using using slinky, slinky, ripple ripple , tank, microwaves, microwaves, or or equationequation E E= =h hf, fwhere, where E Eis isthe the energy energy in in joules, joules, f isf isthe the frequency frequency in in • • WhatWhat is isthe the Doppler Doppler effect? effect? metalmetal becomes becomes ‘white ‘white hot’. hot’. As As it itcools cools down down the the amount amount of of −34 −34 4 4 otherother suitable suitable method. method. hertzhertz and and h his isPlank’s Plank’s constant constant (6.626 (6.626 ×10 ×10 J s).J s). • • Explain,Explain, with with the the aid aid of of labelled labelled diagrams, diagrams, how how this this phenomenon phenomenon radiationradiation drops drops rapidly rapidly (in (in proportion proportion to to T T ) and) and the the peak peak radiation radiation movesmoves from from the the visible visible to to the the infrared infrared and and then then into into the the microwave • • LongitudinalLongitudinal and and transverse transverse waves: waves: frequency, frequency, amplitude, amplitude, occurs.occurs. 1.1. UseUse this this relationship relationship (E ( E= =h hf) fto) to find: find: partpart of of the the spectrum. spectrum. wavelength,wavelength, velocity. velocity. • • DescribeDescribe a alaboratory laboratory experiment experiment to to demonstrate demonstrate the the Doppler Doppler effect. effect. • •the the energy energy of of a photona photon of of orange orange light light of of wavelength wavelength 600 600 nm nm c =c =f λf λ • • InIn fact fact any any object object above above absolute absolute zero zero (e.g. (e.g. a ablock block of of ice) ice) emits emits • • RelationshipRelationship c =c =f λf λ • •the the energy energy of of a aIR IR photon photon of of wavelength wavelength 6000 6000 nm nm InIn the the early early part part of of the the twentieth twentieth century, century, Hubble Hubble and and other other astronomers astronomers suchsuch radiation. radiation. Your Your skin skin (ca. (ca. 32 32 °C) °C) for for instance instance emits emits mostly mostly • • TheThe electromagnetic electromagnetic spectrum spectrum • •the the energy energy of of a amicrowave microwave photon photon of of wavelength wavelength 6 6mm. mm. E E= =h hf f mademade the the first first measurementsmeasurements on on the the spectra spectra from from distant distant stars. stars. They They observedobserved that that these these spectra spectra were were shifted shifted and and they they used used the the Doppler Doppler infraredinfrared radiation radiation (and (and a alittle little microwave microwave radiation) radiation) with with a apeak peak • • DopplerDoppler effect effect frequencyfrequency around around 31 31 THz THz (wavelength (wavelength ca. ca. 9.5 9.5 µm). µm). 2.2. HowHow much much greater greater is isthe the energy energy of of the the orange orange photon photon effecteffect to to explain explain these these shifts. shifts. • • AlthoughAlthough objects objects at at room room temperature temperature emit emit infrared infrared radiation radiation and and thanthan that that of of the the microwave microwave photon photon in in question question 1? 1? • • WhatWhat causes causes the the red red shift shift in in the the spectrum spectrum of of a adistant distant star? star? ScienceScience and and Technology in in Action Action is isalso also widely widely used used microwaves,microwaves, the the total total amount amount is isrelatively relatively small small (about (about 500 500 W W m m −2 ).−2 ). byby Transition Transition Year Year classes. classes. 3.3. InIn Europe Europe mobile mobile phones phones operate operate in in the the 900 900 MHz MHz or or 1800 1800 MHz MHz TheThe yellow yellow line line emitted emitted by by a ahelium helium discharge discharge tube tube in in the the laboratory laboratory has has A Aspecial special device device called called a acavity magnetron is isused used to to generate generate bands.bands. What What are are the the corresponding corresponding wavelengths? wavelengths? a awavelength wavelength of of 587 587 nm. nm. The The same same yellow yellow line line in in the the helium helium spectrum spectrum of of microwavesmicrowaves in in a acontrolled controlled way way at at higher higher powers powers (e.g. (e.g. 100,000 100,000 W). W). a astar star has has a ameasured measured wavelength wavelength of of 590 590 nm. nm. 4.4. UseUse available available information information sources sources to to find find out out details details of ofthe the typical typical • • WhatWhat can can you you deduce deduce about about the the motion motion of of the the star? star? frequency,frequency, power power and and physical physical dimensions dimensions of of radar radar systems systems used used LearningLearning Outcomes Outcomes • • CalculateCalculate the the speed speed of of the the moving moving star. star. forfor long long distance distance aircraft aircraft monitoring. monitoring. Make Make a aposter poster of of other other BiographicalBiographical Notes Notes OnOn completion completion of of this this lesson, lesson, students students should should be be able able to: to: presentationpresentation of of your your findings. findings. • • GiveGive another another application application of of the the Doppler Doppler effect. effect. 8 8 −1 −1 • • OutlineOutline the the main main characteristics characteristics of of waves waves and and particularly particularly of of (speed(speed of of light light = =3.00 3.00 × ×10 10 m m s s) ) 5.5. UseUse available available information information sources sources to to find find out out what what transponders are are electromagneticelectromagnetic waves waves ChristianChristian Hülsmeyer Hülsmeyer (1881–1957) (1881–1957) andand how how they they increase increase the the range range and and usefulness usefulness of of air air traffic traffic ChristianChristian Hülsmeyer Hülsmeyer devised devised the the first first • • ExplainExplain the the term term ‘electromagnetic ‘electromagnetic spectrum’ spectrum’ and and describe describe the the place place controlcontrol systems. systems. Make Make a aposter, poster, or or other other presentation, presentation, of of your your LeavingLeaving Certificate Certificate Physics Physics (OL) (OL) 2006, 2006, Q. Q.12 12 (b) (b) patentedpatented device device that that could could detect detect the the ofof radio radio waves waves in in that that spectrum spectrum findings.findings. presencepresence of of distant distant objects, objects, such such as as ships, ships, • • UseUse the the equation equation c =c =f λf toλ to calculate calculate one one quantity quantity given given the the other other two two TheThe diagram diagram shows shows the the relative relative positions positions of of electromagnetic electromagnetic radiations radiations inin terms terms of of their their wavelength. wavelength. usingusing radio radio waves. waves. His His device, device, which which he he • • OutlineOutline the the principle principle of of radar radar and and describe describe some some of of its its applications applications calledcalled a a‘Telemobiloscope’, ‘Telemobiloscope’, could could not not • • ExplainExplain what what is ismeant meant by by polarisation polarisation of of waves waves gammagamma rays rays AA UVUV lightlight IRIR microwavesmicrowaves BB measuremeasure the the distance distance to to a aship ship and and so so can can • • DescribeDescribe what what is ismeant meant by by the the Doppler Doppler effect effect and and calculate calculate the the hardlyhardly be be called called radar. radar. It Ittransmitted transmitted radio radio DopplerDoppler shift shift given given the the speed speed of of an an object object and and the the source source (i)(i) NameName the the radiations radiations marked marked A Aand and B. B. waveswaves and and when when it itdetected detected the the reflected reflected frequency.frequency. True/FalseTrue/False Questions Questions waveswaves it itactivated activated a abell. bell. Its Its range range was was only only (ii)(ii) GiveGive one one property property which which is iscommon common to to all all electromagnetic electromagnetic a afew few kilometres. kilometres. radiations.radiations. a)a) LightLight travels travels faster faster than than radio radio waves. waves. T T F F HeHe later later developed developed a asystem system that that could could be be (iii)(iii) WhichWhich one one of of the the radiations radiations has has the the shortest shortest wavelength? wavelength? usedused to to find find the the approximate approximate distance distance to to a aship ship which which he he also also patented. patented. b)b) RadioRadio waves waves have have a alower lower frequency frequency than than light light waves. waves. T T F F (iv)(iv) DescribeDescribe how how IR IR radiation radiation is isdetected. detected. HoweverHowever others others were were developing developing pulsed pulsed radar radar systems systems that that measured measured GeneralGeneral Learning Learning Points Points c)c) RadarRadar can can be be used used to to detect detect aircraft aircraft over over 100 100 km km away. away. T T F F thethe time time between between the the transmitted transmitted pulse pulse and and the the returning returning echo echo and and so so (v)(v) GiveGive one one use use for for microwaves. microwaves. indicatedindicated distances distances far far more more accurately. accurately. TheseThese are are additional additional relevant relevant points points which which are are used used to to extend extend d)d) RadarRadar can can be be used used to to detect detect clouds. clouds. T T F F knowledgeknowledge and and facilitate facilitate discussion. discussion. e)e) MarconiMarconi demonstrated demonstrated radar radar in in 1897. 1897. T T F F • • WavesWaves are are propagated propagated from from a asource source and and carry carry energy. energy. f) f) TheThe wavelength wavelength of of a a3 3GHz GHz RF RF signal signal is isone one . metre. T T F F LeavingLeaving Certificate Certificate Physics Physics (HL) (HL) 2014, 2014, Q. Q.10 10 • • ElectromagneticElectromagnetic waves waves do do not not need need a amedium. medium. g)g) TheThe energy energy of of microwave microwave photons photons is isgreater greater than than that that of of BloodBlood pressure pressure can can be be measured measured in in ReviseRevise The The Terms Terms • • LightLight is isone one type type of of electromagnetic electromagnetic wave. wave. visiblevisible light light photons. photons. T T F F manymany ways. ways. One One technique technique uses uses thethe Doppler Doppler effect. effect. CanCan you you recall recall the the meaning meaning of of the the following following terms? terms? • • TheThe electromagnetic electromagnetic spectrum spectrum is isthe the set set of of all all electromagnetic electromagnetic h)h) TheThe energy energy of of a aphoton photon is isproportional proportional to to its its frequency. frequency. T T F F waveswaves and and includes includes radio radio waves waves and and microwaves. microwaves. • • WhatWhat is isthe the Doppler Doppler effect? effect? RevisingRevising terminology terminology is is a apowerful powerful aid aid to to recall recall and and retention. retention. i) i) TheThe radio radio frequency frequency spectrum spectrum includes includes microwaves. microwaves. T T F F • • InIn a avacuum vacuum all all electromagnetic electromagnetic waves waves have have the the same same speed speed (c ).(c). • • Explain,Explain, with with the the aid aid of of labelled labelled acronym,acronym, astronomy, astronomy, binary binary stars, stars, diffracted, diffracted, echo, echo, equilibrium, equilibrium, j) j) TheThe change change in in frequency frequency of of waves waves reflected reflected off off a a movingmoving • • TheThe use use of of the the RF RF (radio (radio frequency) frequency) section section of of the the electromagnetic electromagnetic diagrams,diagrams, how how the the Doppler Doppler frequency,frequency, geology, geology, GHz, GHz, infrared infrared (IR), (IR), meteorology, meteorology, microwaves, microwaves, targettarget is iscalled called the the Marconi Marconi Effect. Effect. T T F F spectrumspectrum is isregulated regulated nationally nationally and and internationally. internationally. Different Different bands bands effecteffect occurs. occurs. millisecond,millisecond, oscillation, oscillation, pitch, pitch, polarised, polarised, propagated, propagated, radar, radar, radio radio areare allocated allocated for for specific specific purposes. purposes. k)k) WhenWhen waves waves travel travel from from one one medium medium to to another another they they can can • • AnAn ambulance ambulance siren siren emits emits a asound sound of of frequency frequency 750 750 Hz. Hz. When When the the frequency,frequency, refracted, refracted, RF, RF, telegraph, telegraph, ultraviolet ultraviolet (UV), (UV), X-rays. X-rays. • • InIn radar radar systems systems a apulsed pulsed radio radio frequency frequency signal signal is isreflected reflected off off a a changechange direction. direction. This This happens happens because because the the frequency frequency of of the the ambulanceambulance is istravelling travelling towards towards an an observer, observer, the the frequency frequency detected detected target.target. The The distance distance to to the the target target can can be be calculated calculated from from the the time time it it waveswaves changes. changes. T T F F byby the the observer observer is is820 820 Hz. Hz. What What is isthe the speed speed of of the the ambulance? ambulance? takestakes for for the the reflected reflected signal signal to to return. return. CheckCheck the the Glossary Glossary of of terms terms for for this this lesson lesson on on www.sta.ie www.sta.ie CheckCheck your your answers answers to to these these questions questions on on www.sta.ie. www.sta.ie. • • StateState two two other other practical practical applications applications of of the the Doppler Doppler effect. effect. • • DopplerDoppler radar radar can can be be used used to to measure measure the the speed speed of of a atarget. target. RadarRadar and and its its uses uses Radar and its uses

SyllabusSyllabus references references StudentStudent Activities Activities ExaminationExamination Questions Questions DidDid You You Know? Know?

TheThe main main syllabus syllabus references references for for the the lesson lesson are: are: ByBy 1905 1905 the the photoelectric photoelectric effect effect had had been been puzzling puzzling scientists scientists for for nearly nearly LeavingLeaving Certificate Certificate Physics Physics (HL) (HL) 2010, 2010, Q. Q.7 7 • • If aIf piecea piece of ofmetal metal is isheated heated and and becomes becomes ‘red ‘red hot’ hot’ it emitsit emits some some 2020 years. years. In InEinstein’s Einstein’s explanation, explanation, published published in in1905 1905 when when he he was was just just visiblevisible red red light light but but considerable considerable more more invisible invisible infrared infrared radiation. radiation. LeavingLeaving Certificate Certificate Physics Physics TheThe Doppler Doppler effect effect applies applies to toall all types types of ofwaves waves and and is isnamed named after after 2626 years years of ofage, age, light light is isconsidered considered to tobe be composed composed of ofparticles particles which which In Infact fact it emitsit emits radiation radiation with with a widea wide range range of ofwavelengths wavelengths with with a a ChristianChristian Johann Johann Doppler, Doppler, an an Austrian Austrian scientist scientist who who explained explained this this hehe called called ‘photons’. ‘photons’. The The energy energy carried carried by by a photona photon depends depends on on its its peakpeak in inthe the IR IR region. region. If itIf isit isheated heated further, further, say say to to1500 1500 °C, °C, the the • • WaveWave phenomena: phenomena: reflection, reflection, refraction, refraction, diffraction, diffraction, interference, interference, phenomenonphenomenon in in1842. 1842. polarisation.polarisation. frequencyfrequency ─ ─which which is isa wavea wave characteristic characteristic ─ ─and and is isgiven given by by the the peakpeak radiation radiation moves moves into into the the visible visible part part of ofthe the spectrum spectrum and and the the • • SimpleSimple demonstrations demonstrations using using slinky, slinky, ripple ripple tank, tank, microwaves, microwaves, or or equationequation E E= =h fh, wheref, where E Eis isthe the energy energy in injoules, joules, f is f isthe the frequency frequency in in • • WhatWhat is isthe the Doppler Doppler effect? effect? metalmetal becomes becomes ‘white ‘white hot’. hot’. As As it coolsit cools down down the the amount amount of of −34 −34 4 4 otherother suitable suitable method. method. hertzhertz and and h ish isPlank’s Plank’s constant constant (6.626 (6.626 ×10 ×10 J s).J s). • • Explain,Explain, with with the the aid aid of oflabelled labelled diagrams, diagrams, how how this this phenomenon phenomenon radiationradiation drops drops rapidly rapidly (in (in proportion proportion to toT T ) and) and the the peak peak radiation radiation movesmoves from from the the visible visible to tothe the infrared infrared and and then then into into the the microwave microwave • • LongitudinalLongitudinal and and transverse transverse waves: waves: frequency, frequency, amplitude, amplitude, occurs.occurs. 1. 1. UseUse this this relationship relationship (E ( E= =h fh) fto) tofind: find: partpart of ofthe the spectrum. spectrum. wavelength,wavelength, velocity. velocity. • • DescribeDescribe a laboratorya laboratory experiment experiment to todemonstrate demonstrate the the Doppler Doppler effect. effect. • the• the energy energy of ofa photona photon of oforange orange light light of ofwavelength wavelength 600 600 nm nm c =c =f λ f λ • • In Infact fact any any object object above above absolute absolute zero zero (e.g. (e.g. a blocka block of ofice) ice) emits emits • • RelationshipRelationship c =c =f λ f λ • the• the energy energy of ofa IRa IR photon photon of ofwavelength wavelength 6000 6000 nm nm In Inthe the early early part part of ofthe the twentieth twentieth century, century, Hubble Hubble and and other other astronomers astronomers suchsuch radiation. radiation. Your Your skin skin (ca. (ca. 32 32 °C) °C) for for instance instance emits emits mostly mostly • • TheThe electromagnetic electromagnetic spectrum spectrum • the• the energy energy of ofa microwavea microwave photon photon of ofwavelength wavelength 6 mm.6 mm. E E= =h fh f mademade the the first first measurements measurements on onthe the spectra spectra from from distant distant stars. stars. They They observedobserved that that these these spectra spectra were were shifted shifted and and they they used used the the Doppler Doppler infraredinfrared radiation radiation (and (and a littlea little microwave microwave radiation) radiation) with with a peaka peak • • DopplerDoppler effect effect frequencyfrequency around around 31 31 THz THz (wavelength (wavelength ca. ca. 9.5 9.5 µm). µm). 2. 2. HowHow much much greater greater is isthe the energy energy of ofthe the orange orange photon photon effecteffect to toexplain explain these these shifts. shifts. • • AlthoughAlthough objects objects at atroom room temperature temperature emit emit infrared infrared radiation radiation and and thanthan that that of ofthe the microwave microwave photon photon in inquestion question 1? 1? • • WhatWhat causes causes the the red red shift shift in inthe the spectrum spectrum of ofa distanta distant star? star? ScienceScience and and Technology Technology in in Action Action is isalso also widely widely used used microwaves,microwaves, the the total total amount amount is isrelatively relatively small small (about (about 500 500 W W m m−2). −2 ). byby Transition Transition Year Year classes. classes. 3. 3. In InEurope Europe mobile mobile phones phones operate operate in inthe the 900 900 MHz MHz or or 1800 1800 MHz MHz TheThe yellow yellow line line emitted emitted by by a heliuma helium discharge discharge tube tube in inthe the laboratory laboratory has has A Aspecial special device device called called a cavitya cavity magnetron magnetron is isused used to togenerate generate bands.bands. What What are are the the corresponding corresponding wavelengths? wavelengths? a wavelengtha wavelength of of587 587 nm. nm. The The same same yellow yellow line line in inthe the helium helium spectrum spectrum of of microwavesmicrowaves in ina controlleda controlled way way at athigher higher powers powers (e.g. (e.g. 100,000 100,000 W). W). a stara star has has a measureda measured wavelength wavelength of of590 590 nm. nm. 4. 4. UseUse available available information information sources sources to tofind find out out details details of theof the typical typical • • WhatWhat can can you you deduce deduce about about the the motion motion of ofthe the star? star? frequency,frequency, power power and and physical physical dimensions dimensions of ofradar radar systems systems used used LearningLearning Outcomes Outcomes • • CalculateCalculate the the speed speed of ofthe the moving moving star. star. forfor long long distance distance aircraft aircraft monitoring. monitoring. Make Make a postera poster of ofother other BiographicalBiographical Notes Notes OnOn completion completion of ofthis this lesson, lesson, students students should should be be able able to: to: presentationpresentation of ofyour your findings. findings. • • GiveGive another another application application of ofthe the Doppler Doppler effect. effect. 8 8 −1 −1 • • OutlineOutline the the main main characteristics characteristics of ofwaves waves and and particularly particularly of of (speed(speed of oflight light = =3.00 3.00 × ×10 10 m ms s) ) 5. 5. UseUse available available information information sources sources to tofind find out out what what transponders transponders are are electromagneticelectromagnetic waves waves ChristianChristian Hülsmeyer Hülsmeyer (1881–1957) (1881–1957) andand how how they they increase increase the the range range and and usefulness usefulness of ofair air traffic traffic ChristianChristian Hülsmeyer Hülsmeyer devised devised the the first first • • ExplainExplain the the term term ‘electromagnetic ‘electromagnetic spectrum’ spectrum’ and and describe describe the the place place controlcontrol systems. systems. Make Make a poster,a poster, or or other other presentation, presentation, of ofyour your LeavingLeaving Certificate Certificate Physics Physics (OL) (OL) 2006, 2006, Q. Q.12 12(b) (b) patentedpatented device device that that could could detect detect the the of ofradio radio waves waves in inthat that spectrum spectrum findings.findings. presencepresence of ofdistant distant objects, objects, such such as as ships, ships, • • UseUse the the equation equation c =c f= λ f toλ tocalculate calculate one one quantity quantity given given the the other other two two TheThe diagram diagram shows shows the the relative relative positions positions of ofelectromagnetic electromagnetic radiations radiations in interms terms of oftheir their wavelength. wavelength. usingusing radio radio waves. waves. His His device, device, which which he he • • OutlineOutline the the principle principle of ofradar radar and and describe describe some some of ofits its applications applications calledcalled a ‘Telemobiloscope’,a ‘Telemobiloscope’, could could not not • • ExplainExplain what what is ismeant meant by by polarisation polarisation of ofwaves waves gammagamma rays rays A A UVUV lightlight IRIR microwavesmicrowaves B B measuremeasure the the distance distance to toa shipa ship and and so so can can • • DescribeDescribe what what is ismeant meant by by the the Doppler Doppler effect effect and and calculate calculate the the hardlyhardly be be called called radar. radar. It transmittedIt transmitted radio radio DopplerDoppler shift shift given given the the speed speed of ofan an object object and and the the source source (i)(i) NameName the the radiations radiations marked marked A Aand and B. B. waveswaves and and when when it detectedit detected the the reflected reflected frequency.frequency. True/FalseTrue/False Questions Questions waveswaves it activatedit activated a bell.a bell. Its Its range range was was only only (ii)(ii) GiveGive one one property property which which is iscommon common to toall all electromagnetic electromagnetic a fewa few kilometres. kilometres. radiations.radiations. a) a) LightLight travels travels faster faster than than radio radio waves. waves. T T F F HeHe later later developed developed a systema system that that could could be be (iii)(iii) WhichWhich one one of ofthe the radiations radiations has has the the shortest shortest wavelength? wavelength? usedused to tofind find the the approximate approximate distance distance to toa shipa ship which which he healso also patented. patented. b) b) RadioRadio waves waves have have a lowera lower frequency frequency than than light light waves. waves. T T F F (iv)(iv) DescribeDescribe how how IR IR radiation radiation is isdetected. detected. HoweverHowever others others were were developing developing pulsed pulsed radar radar systems systems that that measured measured GeneralGeneral Learning Learning Points Points c) c) RadarRadar can can be be used used to todetect detect aircraft aircraft over over 100 100 km km away. away. T T F F thethe time time between between the the transmitted transmitted pulse pulse and and the the returning returning echo echo and and so so (v)(v) GiveGive one one use use for for microwaves. microwaves. indicatedindicated distances distances far far more more accurately. accurately. TheseThese are are additional additional relevant relevant points points which which are are used used to toextend extend d)d) RadarRadar can can be be used used to todetect detect clouds. clouds. T T F F knowledgeknowledge and and facilitate facilitate discussion. discussion. e) e) MarconiMarconi demonstrated demonstrated radar radar in in1897. 1897. T T F F • • WavesWaves are are propagated propagated from from a sourcea source and and carry carry energy. energy. f) f) TheThe wavelength wavelength of ofa 3a GHz3 GHz RF RF signal signal is isone one metre. metre. T T F F LeavingLeaving Certificate Certificate Physics Physics (HL) (HL) 2014, 2014, Q. Q.10 10 • • ElectromagneticElectromagnetic waves waves do do not not need need a medium.a medium. g) g) TheThe energy energy of ofmicrowave microwave photons photons is isgreater greater than than that that of of BloodBlood pressure pressure can can be be measured measured in in ReviseRevise The The Terms Terms • • LightLight is isone one type type of ofelectromagnetic electromagnetic wave. wave. visiblevisible light light photons. photons. T T F F manymany ways. ways. One One technique technique uses uses thethe Doppler Doppler effect. effect. CanCan you you recall recall the the meaning meaning of of the the following following terms? terms? • • TheThe electromagnetic electromagnetic spectrum spectrum is isthe the set set of ofall all electromagnetic electromagnetic h) h) TheThe energy energy of ofa photona photon is isproportional proportional to toits its frequency. frequency. T T F F waveswaves and and includes includes radio radio waves waves and and microwaves. microwaves. • • WhatWhat is isthe the Doppler Doppler effect? effect? RevisingRevising terminology terminology is isa powerfula powerful aid aid to to recall recall and and retention. retention. i) i) TheThe radio radio frequency frequency spectrum spectrum includes includes microwaves. microwaves. T T F F • • In Ina vacuuma vacuum all all electromagnetic electromagnetic waves waves have have the the same same speed speed (c ).(c). • • Explain,Explain, with with the the aid aid of oflabelled labelled acronym,acronym, astronomy, astronomy, binary binary stars, stars, diffracted, diffracted, echo, echo, equilibrium, equilibrium, j) j) TheThe change change in infrequency frequency of ofwaves waves reflected reflected off off a amoving moving • • TheThe use use of ofthe the RF RF (radio (radio frequency) frequency) section section of ofthe the electromagnetic electromagnetic diagrams,diagrams, how how the the Doppler Doppler frequency,frequency, geology, geology, GHz, GHz, infrared infrared (IR), (IR), meteorology, meteorology, microwaves, microwaves, targettarget is iscalled called the the Marconi Marconi Effect. Effect. T T F F spectrumspectrum is isregulated regulated nationally nationally and and internationally. internationally. Different Different bands bands effecteffect occurs. occurs. millisecond,millisecond, oscillation, oscillation, pitch, pitch, polarised, polarised, propagated, propagated, radar, radar, radio radio areare allocated allocated for for specific specific purposes. purposes. k) k) WhenWhen waves waves travel travel from from one one medium medium to toanother another they they can can • • AnAn ambulance ambulance siren siren emits emits a sounda sound of offrequency frequency 750 750 Hz. Hz. When When the the frequency,frequency, refracted, refracted, RF, RF, telegraph, telegraph, ultraviolet ultraviolet (UV), (UV), X-rays. X-rays. • • In Inradar radar systems systems a pulseda pulsed radio radio frequency frequency signal signal is isreflected reflected off off a a changechange direction. direction. This This happens happens because because the the frequency frequency of ofthe the ambulanceambulance is istravelling travelling towards towards an an observer, observer, the the frequency frequency detected detected target.target. The The distance distance to tothe the target target can can be be calculated calculated from from the the time time it it waveswaves changes. changes. T T F F byby the the observer observer is is820 820 Hz. Hz. What What is isthe the speed speed of ofthe the ambulance? ambulance? takestakes for for the the reflected reflected signal signal to toreturn. return. CheckCheck the the Glossary Glossary of of terms terms for for this this lesson lesson on on www.sta.ie www.sta.ie CheckCheck your your answers answers to to these these questions questions on on www.sta.ie. www.sta.ie. • • StateState two two other other practical practical applications applications of ofthe the Doppler Doppler effect. effect. • • DopplerDoppler radar radar can can be be used used to tomeasure measure the the speed speed of ofa target.a target.