Key Concepts: Wave, Transverse wave, Longitudinal/Compressional wave Medium Energy transfer

Transcription

1 PS-7.1 Illustrate ways that the energy f waves is transferred by interactin with matter (including transverse and lngitudinal /cmpressinal waves). Taxnmy Level: 2.2-B Understand Cnceptual Knwledge Key Cncepts: Wave, Transverse wave, Lngitudinal/Cmpressinal wave Medium Energy transfer Previus/Future knwledge: In 8 th grade students recalled that waves transmit energy but nt matter (8-6.1). In Physical Science students will give examples f waves transferring energy withut transferring matter thrugh transverse and lngitudinal/cmpressinal waves. It is essential fr students t Understand that a wave is a repeating disturbance that transfers energy thrugh matter r space. Wave mtin always transfers energy, but nt matter frm ne place t anther. When a wave mves thrugh matter, the matter is disturbed s that it mves back and frth, but after the wave passes, the matter will be in abut the same psitin that it was befre the wave passed. Give general examples f varius waves, illustrating, with diagrams r descriptins, the directin f the disturbance and the mtin f the particles f the medium in each. Each illustratin shuld: Describe the energy (light, sund, mechanical disturbance, etc); Describe the directin and the path that the energy takes; Identify the medium, if any; Describe the directin that the particles f the medium are disturbed as the wave passes; Describe the psitin f the particles f the medium befre and after the wave passes. Examples f illustratins may include: Slinky waves - transverse and/r lngitudinal (see PS-7.2). A wave in a slinky spring illustrates a mechanical disturbance caused by a frce displacing ne f the spring cils. The energy f a wave in a slinky spring will pass frm the pint n the spring where a cil has been displaced t the end f the slinky. The medium cnsists f the slinky cils. The cils either mve back and frth parallel t the length f the spring, r back and frth perpendicular t the length f the spring Effective September 2007 All indicatrs in Standard PS 7 1 / 16

2 After the wave passes, the cils return t apprximately the psitin where they were befre the wave passed. Sund waves: The energy f the wave transmits frm the tuning frk ut in all directins. The shape f the wave will apprximate the shape f cncentric spheres. A sund wave requires a medium thrugh which it travels. A sund wave is a lngitudinal mechanical disturbance caused by a frce displacing mlecules in the medium thrugh which it passes. A sund wave's energy travels ut in all directins frm a vibrating bject. A sund wave travels thrugh the medium. The particles f the medium remain where they were riginally, but the wave energy mves frm ne place t anther. The particles f the medium mve back and frth, parallel t the directin f the wave. After a sund wave passes, the particles f the medium cntinue mving in apprximately the same area where they were befre the wave passed. Light waves Light waves d nt need a medium thrugh which t travel. Light waves are transverse waves. Light waves (r ther electrmagnetic waves) are energy that can be transmitted withut mechanical disturbance f the particles f a medium Light waves (and ther electrmagnetic waves) travel in straight lines in all directins frm the surce f the light as lng as the medium des nt change. Light waves can transmit energy thrugh empty space as frm the Sun r stars. The energy f the light wave travels frm ne place t anther, but the particles f the medium, if there is ne, remain in apprximately the same area where they were befre the wave passed. Effective September 2007 All indicatrs in Standard PS 7 2 / 16

3 Students shuld understand that all waves transfer energy frm place t place. If the wave mves thugh a medium, the particles f the medium can be displaced in a variety f ways (such as parallel r perpendicular t the wave mtin), but they are nt transprted with the energy f the wave. Assessment Guidelines: The bjective f this indicatr is t illustrate ways that the energy f waves is transferred, therefre, the primary fcus f assessment shuld be t find specific illustratins (drawings, diagrams, r wrd descriptins) r use illustratins that shw that the energy is being transferred in a variety f waves, transverse and lngitudinal/cmpressinal, and hw the transfer f energy is different frm the displacement f particles in the medium. In additin t illustrate, students shuld be able t Identify transverse and lngitudinal waves frm illustratins; Cmpare transverse and lngitudinal wave particle mtin and energy transfer directin; Summarize the characteristics f lngitudinal/transverse waves. Exemplify transverse and lngitudinal waves. Effective September 2007 All indicatrs in Standard PS 7 3 / 16

4 PS-7.2 Cmpare the nature and prperties f transverse and lngitudinal/cmpressinal mechanical waves. Taxnmy level: 2.6-B Understand Cnceptual Knwledge Key Cncepts: Mechanical waves: Transverse waves, Lngitudinal/Cmpressinal waves Wave prperties: Crest, Trugh; Cmpressin, Rarefactin Previus/Future knwledge: In the 8 th grade students distinguished between mechanical and electrmagnetic waves (8-6.2), and explained hw scientists use seismic waves primary, secndary, and surface waves t determine the internal structure f Earth (8-3.2). In Physical Science students will cnsider particle mvement within the medium t cmpare transverse and lngitudinal waves. It is essential fr students t Understand that there are tw types f waves, electrmagnetic and mechanical. Electrmagnetic waves may travel thrugh a medium but d nt need a medium fr transmissin. Electrmagnetic waves transfer energy thrugh a medium r space. (Electrmagnetic waves will be addressed in PS-7.5) Mechanical waves must have a medium thrugh which t mve. Mechanical waves transfer energy thrugh the particles f a medium. The particles f the medium mve back and frth, but the wave (energy) itself is transmitted prgressively frm ne place t anther. Understand the nature f transverse and lngitudinal mechanical waves. In a transverse wave, as the wave (energy) mves thrugh the medium, the directin f the back and frth mtin f the particles is perpendicular t the directin that the wave is mving. Examples f transverse mechanical waves might include: Sme slinky spring waves, secndary earthquake waves, and waves in the string f stringed instruments such as a guitar. In a lngitudinal wave (als called cmpressinal), as the wave (energy) mves thrugh the medium, the directin f the back and frth mtin f the particles is parallel t the directin that the wave is mving. Examples f lngitudinal mechanical waves might include: Sme slinky spring waves, sund waves, primary earthquake waves, shck waves frm a snic bm r explsin, and ultrasnic waves. Understand the wave prperties f transverse waves - crests and trughs, and f lngitudinal waves - cmpressins and rarefactins. In a transverse wave the pint f maximum displacement f the particles in a medium frm the equilibrium psitin is called a crest r trugh. In a lngitudinal wave the particles f the medium are pushed clser tgether t frm a high pressure area called a cmpressin and spread ut t frm a lwer pressure area with fewer particles called a rarefactin. Understand that sme waves cannt be classified as transverse r lngitudinal waves The mtin f the particles in sme waves can be described as circular. Surface water waves fall int this categry. In trsin waves the mtin f the particles is a twisting mtin. Effective September 2007 All indicatrs in Standard PS 7 4 / 16

5 Miscnceptin: Students smetimes think that waves are ne r tw-dimensinal. Many waves such as sund and light waves are ften three-dimensinal. It is nt essential fr students t describe the mtin f particles in waves that are nt transverse r lngitudinal waves, such as trsin waves r water surface waves. Students shuld, hwever, be able t recgnize these waves as nn-examples if the mtin f the particles in the medium is described. Assessment Guidelines: The bjective f this indicatr is t cmpare the nature and prperties f transverse and lngitudinal waves, therefre, the primary fcus f assessment shuld be t give similarities and differences between these waves with regard t the mvement f the particles in the medium, the directin that the wave mves, and the prperties f the waves. In additin t cmpare, students shuld be able t Exemplify r Illustrate transverse and lngitudinal waves - give examples r draw r label illustratins which depict the mtin f particles and the mtin f the wave; Classify waves by determining which f the tw types f waves (transverse r lngitudinal) is being described based n the mtin f particles and the mtin f the wave; Summarize transverse and lngitudinal mechanical waves by giving majr pints abut the characteristics f these waves. Effective September 2007 All indicatrs in Standard PS 7 5 / 16

6 PS-7.3 Summarize characteristics f waves (including displacement, frequency, perid, amplitude, wavelength, and velcity as well as the relatinships amng these characteristics). Taxnmy Level: 2.4-B Understand Cnceptual Knwledge Key Cncepts: Displacement f particles Frequency: Hertz Perid Amplitude Wavelength Velcity - meaning speed Previus/Future knwledge: In the 8 th grade students summarize factrs that influence the basic prperties f waves (including frequency, amplitude, wavelength, and speed) (8-6.1). In Physical Science the students expand n this idea and summarize the relatinships amng these characteristics. Students will understand the relatinship f the mvement f the particles in the medium and the wave characteristics. In Physical Science the cncept f displacement is intrduced bth with respect t the wave energy and with respect t the mvement f the particles in the medium. It is essential fr students t Understand characteristics f waves can be explained in terms f hw the particles in the medium behave. Amplitude The amplitude is the greatest displacement f the particles in a wave frm their equilibrium (rest) psitin. In a transverse wave amplitude is measured frm the equilibrium r rest psitin f the medium t a crest r trugh. Displacement Displacement with respect t waves will refer t the displacement f the particles in the medium. This quantity has magnitude and directin. It is the distance f a vibrating particle frm the midpint f its vibratin. (Displacement is used in discussing amplitude and interference f mechanical waves.) Frequency The frequency f the wave is the number f cmplete cycles (r vibratins) the particles g thrugh per secnd r the number f waves that pass a pint per secnd. The unit fr frequency is Hertz, which is ne vibratin per secnd r ne cycle per secnd r ne wave per secnd. The frequency and the wavelength are inversely related. When the frequency gets higher the wavelength gets shrter. Effective September 2007 All indicatrs in Standard PS 7 6 / 16

7 Perid The perid f a wave is the time fr ne cycle (r vibratin) r the time fr ne cmplete wave t pass a pint. The perid is usually measured in secnds. The perid and the frequency are inversely related. An increase in frequency wuld result in a decrease in perid. Wavelength Wavelength f a wave is distance between a pint in a wave and the next similar (in phase) pint. In a transverse wave the wavelength can be measured frm a crest t the next crest r frm a trugh t the next trugh. In a lngitudinal wave the wavelength can be measured frm pint in the cmpressin t a similar pint in the next cmpressin r frm a rarefactin t a similar pint in the next rarefactin. Teacher Nte: Since mst lngitudinal waves (such as sund waves) are nt visible, the wavelength is ften measured by indirect means. Velcity/Speed The velcity/speed f the wave is a functin f the medium and the type f wave and will nt change unless the characteristics f the medium r type f wave changes. Changes in frequency r wavelength d nt affect the velcity/speed (f mechanical waves). When ne f these increases the ther decreases and the prduct f the tw is a cnstant, which is the velcity/speed. When the medium changes, the speed f waves changes. Examples may include: Sund travels faster in steel than in air. Sund travels faster in warm air than cler air. Light travels faster in air than in glass. Transverse waves travel slwer in a heavy rpe than in a light rpe. Teacher nte: Fr purpses f this curse wave velcity/speed will be treated as a scalar quantity. N directin needs t be indicated. It is nt essential fr students t Knw the speed f waves in certain media; Explain why waves travel slwer in ne specific medium than anther. Assessment Guidelines: The bjective f this indicatr is t summarize the characteristics f waves, therefre, the primary fcus f assessment shuld be t give majr pints abut each characteristic f a wave and the relatinships amng these characteristics. In additin t summarize, assessments may require that students Cmpare the characteristics f different types f waves; Exemplify and illustrate characteristics f different types f waves; Identify wave characteristics frm a descriptin r diagram; Interpret diagrams t determine wave characteristics. Effective September 2007 All indicatrs in Standard PS 7 7 / 16

8 PS-7.4 Use the frmulas v = f λ and v = d/t t slve prblems related t the velcity f waves. Taxnmy Level: 3.2-C Apply Prcedural Knwledge Key Cncepts: Wave speed Hertz Frequency Wavelength Previus/Future knwledge: In the 8 th grade students used the frmula fr average speed, v = d/t, t slve real-wrld prblems (8-5.2). The students used this frmula fr finding speed f bjects. Students have nt previusly used these frmulas applied t waves. In Physical Science students will use the frmulas v = f λ and v = d/t in different and unfamiliar situatins t slve prblems relating t all f the variables in the indicatr with respect waves. It is essential fr students t Slve prblems fr any variables in the tw equatins, v = f λ (f = v/ λ r λ = v/f ) and v = d/t (d = v t r t = d/v), using experimental data. Use dimensinal analysis t determine the prper units. Examples may include: If distance is given in meters and time is given in secnds, then velcity will be m/s. If frequency is given in hertz and wavelength is given in meters, then velcity will be m/s. If velcity is given in km/h and time is given in hurs then distance will be kilmeters. Fr math prblems invlving the wave standard in Physical Science, the quantities are treated as scalar quantities (have size r amunt nt directin) rather than vectr quantities that wuld invlve directin. Fr the purpses f the wave prblems, v will represent the scalar quantity speed. Fr the purpses f the wave prblems, d will represent the scalar quantity distance. It is nt essential fr students t Slve prblems invlving bth frmulas - finding a factr in ne frmula t use in the ther frmula; Slve vectr prblems (speed and directin) invlving waves. Assessment Guidelines: The bjective f this indicatr is t use the frmulas v = f λ and v = d/t t slve prblems, therefre, the primary fcus f assessment shuld be t apply the crrect prcedure t mathematically determine ne f the variables in the frmulas v = f λ and v = d/t. In additin t use, assessments may require that students Use dimensinal analysis t determine crrect units; Recgnize symbls and units fr wave velcity frmulas. Effective September 2007 All indicatrs in Standard PS 7 8 / 16

9 PS-7.5 Summarize the characteristics f the electrmagnetic spectrum (including range f wavelengths, frequency, energy, and prpagatin withut a medium). Taxnmy Level: 2.4-B Understand Cnceptual Knwledge Key Cncepts: Electrmagnetic spectrum Visible spectrum Prpagatin withut a medium Previus/Future knwledge: In the 8 th grade students cmpared the wavelength and energy f waves in varius parts f the electrmagnetic spectrum (including visible light, infrared, and ultravilet radiatin) (8-6.8). Physical Science requires that students expand their cncept f the nature f electrmagnetic radiatin. Students will summarize different types f radiatin within the spectrum. It is essential fr students t understand That there is a wide range f frequencies and wavelengths f electrmagnetic waves. The entire range f frequencies is called the electrmagnetic spectrum. The relative psitins f the different types f electrmagnetic waves n the spectrum. Students shuld knw the rder f electrmagnetic waves frm lw frequency t high frequency: radi waves, micrwaves, infrared radiatin, visible light (red, range, yellw, green, blue, vilet), ultravilet, X-rays, and gamma rays. Understand that the energy f electrmagnetic waves is directly prprtinal t the frequency. When listed in rder frm lwest energy t highest energy, the list is the same as when listed frm lwest frequency t highest. Electrmagnetic waves with higher frequencies than visible light als have mre energy. This is why ultravilet light can burn yur skin, and X-rays and gamma can damage tissues. Electrmagnetic waves with lwer frequencies than visible light and have less energy than visible light. Understand that the higher frequency electrmagnetic waves have shrter wavelengths. Understand that wavelengths vary greatly frm very lng wavelengths (many meters) t very shrt wavelengths (the size f atmic nuclei). Understand that electrmagnetic waves travel in space with n medium r may travel thrugh a transparent medium. All types f electrmagnetic waves travel at the same speed in a vacuum. Electrmagnetic waves slw dwn when they mve frm a vacuum t a transparent medium. Electrmagnetic waves are transverse waves. It is nt essential fr students t Explain the nature f the scillating electric and magnetic fields in electrmagnetic waves; Give the specific numbers fr the wavelength r frequency range f different types f electrmagnetic waves; Understand the cncept f phtns f energy, but this may be a gd class discussin depending n the level f the students; Understand hw different spectra (cntinuus, bright line/emissin, dark line/absrptin) are prduced. Effective September 2007 All indicatrs in Standard PS 7 9 / 16

10 Assessment Guidelines: The bjective f this indicatr is t summarize the characteristics f the electrmagnetic spectrum, therefre, the primary fcus f assessment shuld be t give majr pints abut the wavelengths, frequency, energy, and prpagatin withut a medium fr the different types f electrmagnetic radiatin. In additin t summarize, assessments may require that students: Cmpare the frequency, wavelength, and energy f different types f electrmagnetic radiatin; Infer characteristics f a type f electrmagnetic radiatin frm its psitin in the spectrum; Exemplify characteristics and types f electrmagnetic radiatin; Illustrate r use illustratin t shw characteristics f waves at different psitins n the electrmagnetic spectrum. Effective September 2007 All indicatrs in Standard PS 7 10 / 16

11 PS-7.6 Summarize reflectin and interference f bth sund and light waves and the refractin and diffractin f light waves. Taxnmy Level: 2.4-B Understand Cnceptual Knwledge Key Cncepts: Wave behavirs: Reflectin, Refractin, Diffractin Cnstructive interference, Destructive interference Cncave lens, Cnvex lens Law f reflectin, Plain mirrrs Previus/Future knwledge: In the 8 th grade students summarized the behavirs f waves (including refractin, reflectin, transmissin, and absrptin) (8-6.4); explained hearing in terms f the relatinship between sund waves and the ear. (8-6.5); explained sight in terms f the relatinship between the eye and the light waves emitted r reflected by an bject (8-6.6); and explain hw the absrptin and reflectin f light waves by varius materials result in the human perceptin f clr (8-6.7). In Physical Science the students will expand the ideas f reflectin and refractin f light and reflectin f sund. The students will be intrduced t the ideas f cnstructive and destructive interference f sund and light waves. The students will als be intrduced t the cncept f diffractin f light waves. It is essential fr students t Understand that waves can interfere with each ther when they pass thrugh a medium simultaneusly. The result f the cmbinatin f the waves when they pass thrugh the medium simultaneusly can shw cnstructive and/r destructive interference. Interference may be cnstructive: A crest will interfere with anther crest cnstructively t prduce a larger crest and a trugh will interfere with anther trugh t prduce a larger trugh. Cmpressins interfere cnstructively with each ther as d rarefactins. Interference may be destructive: A crest will interfere with a trugh t lessen r cancel the displacement f each. Cmpressins interfere with rarefactins t lessen r cancel the displacement f each The individual waves are nt affected by the interference and will cntinue n as if nthing has happened. Sund waves It is essential fr students t Understand that sund is a lngitudinal mechanical wave, requires a medium, and can be prduced by vibrating bjects. Understand that sund, like ther waves, reflects (bunces ff a surface it cannt g thrugh). Sund prduces eches when it bunces ff hard surfaces. Understand that sund waves interfere with each ther changing what yu hear. Destructive interference makes sunds quieter; cnstructive interference makes sunds luder. This is because amplitude f a wave is what is affected by interference and a sund wave s amplitude is heard as ludness. Sund waves reflect in tubes r sme musical instruments t prduce standing waves which reinfrce sund thrugh cnstructive interference t make the sund luder. Effective September 2007 All indicatrs in Standard PS 7 11 / 16

12 Light waves It is essential fr students t Understand that light waves reflect: When light rays reflect they bey the Law f Reflectin. The angle f incidence is equal t the angle f reflectin. The angle f incidence is the angle between the incident ray and a line nrmal (perpendicular) t the surface at the pint where the light strikes. The angle f reflectin is the angle between the reflected ray and the nrmal line. Understand that light waves reflect in plain mirrrs t prduce images. The image appears as far behind the mirrr as the bject is in frnt f it. The image and the bject appear t be same size. The image is upright. Understand that light, like ther waves, can diffract. Diffractin is the bending f a wave arund a barrier r arund the edges f an pening. Waves with a lnger wavelength diffract mre readily. In rder t bserve light diffractin the barriers r penings must be small. When light waves diffract interference patterns can ften be bserved. Understand that light waves can interfere t prduce interference patterns. Light waves can interfere cnstructively and destructively. When light waves interfere, a pattern is ften seen with light and dark areas created by cnstructive and destructive interference. The amplitude f a light wave is bserved as brightness. Brighter areas shw cnstructive interference and darker areas shw destructive interference. At ther times light waves interfere t prduce a clr pattern. When a clr f light interferes destructively, we will nt see that clr. We will see the clrs that are nt interfered with destructively. Light waves can reflect ff the bttm and tp surfaces f thin film, such as il n water r bubbles, and prduce a clr pattern due t interference. Light wave can diffract thrugh small slits r arund lines t prduce light and dark patterns r clr patterns due t the interference f light waves. Understand that light, like ther waves, can refract. Waves refract when they change directin upn entering anther medium. In rder t refract the wave must: Change speed when it hits the new medium and The wave must strike the new medium at an angle ther than perpendicular. Light waves refract when they enter a different medium at an angle ther than perpendicular and change speed. Students shuld be able t predict the way that the light rays will bend. In the diagram at the right, light slws dwn when it enters the prism and bends dwn when it strikes at this angle. When light exits the prism at the right, it speeds back up and bends dwn again. Effective September 2007 All indicatrs in Standard PS 7 12 / 16

13 When white light enters anther medium such as a prism and refracts the clrs may spread ut. This is because the vilet end f the spectrum slws dwn mre than the red end and therefre bends mre. Lenses may be a cncave (diverging) lens r cnvex (cnverging) lens. Students shuld be able t draw the resulting rays as light passes thrugh each type f lens. It is nt essential fr students t Understand the distance an bject must be placed t prduce certain images with different types f lenses r mirrrs r the sizes f thse images; Understand cncave and cnvex mirrrs; Understand fcal length; Understand that light waves frm real r virtual images f different sizes when passing thrugh lenses; Understand hw sund waves are made by musical instruments. Assessment Guidelines The bjective f this indicatr is t summarize the cncepts f reflectin, refractin, diffractin and interference fr light waves and reflectin and interference fr sund waves, therefre, the primary fcus f assessment shuld be give majr pints abut these wave behavirs related t light and sund waves. In additin t summarize, assessments may require that students Cmpare the behavir f light waves in different situatins f reflectin r refractin; Infer hw light waves reflect, refract r interfere; Infer what will be heard when sund interferes r reflects; Exemplify behavir f light r sund waves in different situatins r effects f that behavir; Illustrate light wave behavir when it encunters cncave r cnvex lenses r a prism. Effective September 2007 All indicatrs in Standard PS 7 13 / 16

14 PS-7.7 Explain the Dppler effect cnceptually in terms f the frequency f the waves and the pitch f the sund. Taxnmy Level: 2.7-B Understand Cnceptual Knwledge Key Cncepts: Dppler Effect Frequency, Wavelength, Pitch Previus/Future knwledge: In the 8 th grade students explained hearing in terms f the relatinship between sund waves and the ear (8-6.5). In Physical Science the students will expand their cncept f wave frequency and hw they hear frequency f sund as pitch by explaining the Dppler effect. It is essential fr students t Understand that the Dppler effect is an apparent frequency shift due t the relative mtin f an bserver and a wave surce. Understand the relative mtin f a wave surce and an bserver. A Dppler shift ccurs when a wave surce is mving tward an bserver r away frm the bserver. A Dppler shift als ccurs when the bserver is mving tward r away frm the wave surce. There is n shift when the surce and bserver are nt mving tward r away frm each ther. Observer A Observer B Waves frm a surce that is nt mving. The example abve shws a wave surce and bservers that are nt mving relative t ne anther. If the wave surce in the example is a sund wave, bserver A and bserver B wuld hear the same pitch (frequency) that the surce is prducing. Effective September 2007 All indicatrs in Standard PS 7 14 / 16

15 Observer A Observer B The example abve shws a wave surce that is mving tward bserver B. If the wave surce in the example is a sund wave then bserver B will hear a higher pitch (frequency) and bserver A will hear a lwer pitch (frequency) than the surce is actually prducing. Situatin wave surce mving tward r away frm an bserver: As a wave surce appraches an bserver, the bserver perceives a higher frequency than the surce is prducing. Wavelengths are shrter and the frequency is higher in frnt f a mving surce. The surce f the wave is catching up with the wave in frnt f it. When it prduces the next pulse the resulting wavelength is shrter. A shrter wavelength means that there will be a higher frequency If the wave is a sund wave, the bserver will perceive a pitch that is higher than the pitch prduced by the surce. When the wave surce is mving away frm the bserver, he/she will perceive a lwer frequency than the surce in prducing. Wavelengths are lnger and the frequency is lwer behind a mving surce. The surce f the sund is mving away frm the wave behind it. When it prduces the next pulse the resulting wavelength is lnger. A lnger wavelength means that there will be a lwer frequency. If the wave is a sund wave, the bserver will perceive a lwer pitch that the surce is prducing Situatin the bserver mving tward r away frm the wave surce: When the bserver is mving tward a wave surce, he/she wuld perceive a higher frequency than the surce is prducing. The bserver encunters waves mre ften than the surce is prducing them. If the bserver encunters mre waves, he/she perceives a higher frequency. The bserver wuld perceive a higher pitch in the case f sund waves. When the bserver is mving away frm a wave surce he/she wuld perceive a lwer frequency than the surce is prducing. The waves wuld have t catch up with him and he/she wuld encunter fewer waves. Waves frm a surce that is mving t the right. If the bserver encunters fewer waves he/she perceives a lwer frequency. The bserver wuld perceive a lwer pitch in the case f sund waves. Effective September 2007 All indicatrs in Standard PS 7 15 / 16

16 Miscnceptin: Students smetimes say that the Dppler effect is bserved when a surce f sund and an bserver mve tward each ther the sund gets luder and as they mve away frm each ther the sund gets sfter. While the bserver will hear a luder and sfter sund in these situatins, this is nt the Dppler effect. It nt essential fr students t understand why a red shift r blue shift ccurs in light. Assessment Guidelines: The bjective f this indicatr is t explain the Dppler effect in terms f frequency and pitch, therefre the primary fcus f assessment shuld be t cnstruct cause and effect mdels that shw the effect each variable has n the perceived frequency f waves and n the pitch f sund. Assessments shuld be based n the fact that the relative mtin between a surce f waves and an bserver will affect the frequency at which waves are encuntered. An bserver will perceive a different frequency (pitch with sund) than the frequency f the surce. In additin t explain, assessments may require that students Identify the frequency that the listener bserves in different situatins relative t the frequency that the surce is prducing r the pitch heard by different bservers in different lcatins with respect t the wave surce; Summarize hw different situatins affect the perceptin f relative pitch (frequency); Infer frm situatins the relative pitch that the listener will bserve; Exemplify situatins which will prduce the Dppler effect with sund waves. Effective September 2007 All indicatrs in Standard PS 7 16 / 16