acoustics - Doppler effect "apparent frequency" - Physics Stack Exchange up vote 2 down vote accepted Actually No. Here's a Flash simulation for Doppler effect which I found useful while googling. It really does exist and not some random appearance..! I don't know whether the term Apparent frequency is good to use or not... We know that Sound is a form of mechanical vibration. When the source moves away from the stable observer at some noticeable speeds (relative to observer) or the observer moves away from the stable source, the frequency of sound perceived by the observer is always less than the actual frequency of the source. It could be easily imagined when you stand somewhere along the roadside and a speeding car passes by... (which is provided in Scene 1 of the simulation). For the reversal (i.e. either the observer or the source moving towards each other), it happens exactly antonymous... One thing to notice in Doppler effect is that when the observer speeds at the speed of sound relative to the source, his detector (ear) doesn't oscillate at all. I mean, you'd probably hear Nothing...

up vote 4 down vote I would have to see the words in context, but the description "apparent frequency" seems strange to me. The frequency your ear detects is exactly what the most sophisticated scientific instrument would measure. The Doppler shift is real in that the frequency your ear detects is really the sound frequency in your frame. I would guess "apparent frequency" means that in your frame the frequency of the source is different to the frequency measured in the rest frame of the source. So you could argue that in your frame the frequency of the source "appears" to be different. However I would argue that it doesn't just "appear" to be different, it really is different! You'll find the same sort of confusion when you start learning special relativity. In your inertial frame an object moving at nearly the speed of light has its length contracted , that is you will measure the moving object to be shorter than someone making the same measurement in the object's rest frame. But there's nothing "apparent" about it: in your frame the object really is shorter.

Doppler effect - definition of Doppler effect by The Free Dictionary Doppler effect - definition of Doppler effect by The Free Dictionary Related to Doppler effect: Doppler radar , CT scan , MRI Dop·pler effect (dŏp′lər) n. A change in the observed frequency of a wave, as of sound or light, occurring when the source and observer are in motion relative to each other, with the frequency increasing when the source and observer approach each other and decreasing when they move apart. The motion of the source causes a real shift in frequency of the wave, while the motion of the observer produces only an apparent shift in frequency. Also called Doppler shift. [After Christian Andreas Doppler (1803-1853), Austrian physicist and mathematician who explained the phenomenon.] Doppler effect (ˈdɒplə) n (General Physics) a phenomenon, observed for sound waves and electromagnetic radiation, characterized by a change in the apparent frequency of a wave as a result of relative motion between the observer and the source. Also called: Doppler shift [C19: named after C. J.

Doppler (1803–53), Austrian physicist] Dop′pler effect` (ˈdɒp lər) n. a phenomenon characterized by a change (Dop′pler shift`) in the frequency of waves, as light or sound waves, observed when the wave source is moving relative to the observer. [1900–05; after C. J. Doppler (1803–53), Austrian physicist] Doppler effect As the source of sound waves (the ambulance) moves closer to the observer, the frequency of the sound waves and pitch of the sound become higher. As the source moves away from the observer, the frequency and pitch become lower. Dop·pler effect (dŏp′lər) The apparent change in the frequency of waves, as of sound or light, when the source of the waves is moving toward or away from an observer. Did You Know? When a car rushes past you on the road with the driver holding down the horn, you hear the horn change tone: it's higher pitched than normal as the car approaches and lower pitched as it departs. That's because of the Doppler effect. Sound waves spread outward in all directions from the horn.

The forward motion of the car compresses the sound waves traveling ahead of the car, making the wavelengths shorter. Sound having shorter wavelengths has higher frequency and therefore higher pitch—what you hear if the car is moving towards you. Behind the car, however, the sound waves are drawn apart. Longer wavelengths mean lower frequency and lower pitch, which is what you hear once the car rushes past. The Doppler effect works on light waves, too; in fact, this was how scientists determined that the universe is expanding. The light from galaxies and other distant celestial objects is shifted toward the red end of the spectrum (a phenomenon called red shift). Red light has the longest wavelengths of visible light. The pioneering astronomer Edwin Hubble reasoned that the red shift was due to the Doppler effect: the galaxies are speeding away from us, drawing out the wavelengths of the light emitted behind them, and the universe as a whole is expanding. doppler effect The phenomenon evidenced by the change in the observed frequency of a sound or radio wave caused by a time rate of change in the effective length of the path of travel between the source and the point of observation.

döppler effect Apparent change in the frequency of light waves or sound waves due to the relative motion of the observer and the source of the waves. ThesaurusAntonymsRelated WordsSynonymsLegend: PhysicsLAB: The Doppler Effect The Doppler Effect Printer Friendly Version The Doppler Effect is the apparent change in a wave's frequency resulting from the relative velocity between the source of the waves and the observer. Although the Doppler Effect is generally associated with sound waves, it is applicable to any type of wave. As a rule of thumb, if the distance between the source and the observer decreases, the apparent frequency (called "f prime" or f') is higher than the actual, real frequency of the source. Case 1: Observer moving. If the observer is moving but the source is stationary, the apparent frequency change is evidenced directly and can be calculated with the formula: Δf is the apparent change in frequency, f is the original frequency, v is the velocity of the observer with respect to the stationary source, vw is the speed of the wave.

To calculate the final frequency the observer records you would use the relationships: when the observer approaches a wave source: f ' = f + Δf --- a higher frequency when the observer recedes from a wave source: f ' = f - Δf --- a lower frequency Remember that the actual frequency of the source remains unchanged and that this apparent change in frequency is due to the relative velocity between the source and the observer. Also remember that it is the frequency that is manipulated mathematically when the observer is moving either towards or away from the source. An analogy. Suppose that you are a parent watching your child play at the beach. If the child stands still in the shallow water, you note that one wave reaches your child's position each second. However, suppose that the child decides to "rush out to meet" the waves. The child will encounter the waves more frequently as he rushes out towards the deeper water. Instead of one wave reaching him each second, he might meet two or three each second. Conversely, if the child "runs away from the waves" back into the shore, instead of one wave reaching him every second, a wave might only reach him once every 1.5 to 2 seconds.

The child can change the "apparent frequency" of the oncoming waves through his motions. How much the frequency changes depends on the child's relative speed. The Doppler Effect and Shock Waves Sound Waves and Music - Lesson 3 Behavior of Sound Waves The Doppler Effect and Shock Waves Reflection, Refraction, and Diffraction The Doppler effect is a phenomenon observed whenever the source of waves is moving with respect to an observer. The Doppler effect can be described as the effect produced by a moving source of waves in which there is an apparent upward shift in frequency for the observer and the source are approaching and an apparent downward shift in frequency when the observer and the source is receding. The Doppler effect can be observed to occur with all types of waves - most notably water waves, sound waves, and light waves. The application of this phenomenon to water waves was discussed in detail in Unit 10 of The Physics Classroom Tutorial . In this unit, we will focus on the application of the Doppler effect to sound. We are most familiar with the Doppler effect because of our experiences with sound waves. Perhaps you recall an instance in which a police car or emergency vehicle was traveling towards you on the highway.

As the car approached with its siren blasting, the pitch of the siren sound (a measure of the siren's frequency) was high; and then suddenly after the car passed by, the pitch of the siren sound was low. That was the Doppler effect - a shift in the apparent frequency for a sound wave produced by a moving source. Another common experience is the shift in apparent frequency of the sound of a train horn. As the train approaches, the sound of its horn is heard at a high pitch and as the train moved away, the sound of its horn is heard at a low pitch. This is the Doppler effect. A common Physics demonstration the use of a large Nerf ball equipped with a buzzer that produces a sound with a constant frequency. The Nerf ball is then thrown around the room. As the ball approaches you, you observe a higher pitch than when the ball is at rest. And when the ball is thrown away from you, you observe a lower pitch than when the ball is at rest. This is the Doppler effect. Explaining the Doppler Effect The Doppler effect is observed because the distance between the source of sound and the observer is changing.

If the source and the observer are approaching, then the distance is decreasing and if the source and the observer are receding, then the distance is increasing. The source of sound always emits the same frequency. Therefore, for the same period of time, the same number of waves must fit between the source and the observer. if the distance is large, then the waves can be spread apart; but if the distance is small, the waves must be compressed into the smaller distance. For these reasons, if the source is moving towards the observer, the observer perceives sound waves reaching him or her at a more frequent rate (high pitch). And if the source is moving away from the observer, the observer perceives sound waves reaching him or her at a less frequent rate (low pitch). It is important to note that the effect does not result because of an actual change in the frequency of the source. The source puts out the same frequency; the observer only perceives a different frequency because of the relative motion between them. The Doppler effect is a shift in the apparent or observed frequency and not a shift in the actual frequency at which the source vibrates.

Shock Waves and Sonic Booms The Doppler effect is observed whenever the speed of the source is moving slower than the speed of the waves. But if the source actually moves at the same speed as or faster than the wave itself can move, a different phenomenon is observed. If a moving source of sound moves at the same speed as sound, then the source will always be at the leading edge of the waves that it produces. The diagram at the right depicts snapshots in time of a variety of wavefronts produced by an aircraft that is moving at the same speed as sound. The circular lines represent compressional wavefronts of the sound waves. Notice that these circles are bunched up at the front of the aircraft. This phenomenon is known as a shock wave. Shock waves are also produced if the aircraft moves faster than the speed of sound. If a moving source of sound moves faster than sound, the source will always be ahead of the waves that it produces. The diagram at the right depicts snapshots in time of a variety of wavefronts produced by an aircraft that is moving faster than sound. Note that the circular compressional wavefronts fall behind the faster moving aircraft (in actuality, these circles would be spheres).

If you are standing on the ground when a supersonic (faster than sound) aircraft passes overhead, you might hear a sonic boom. A sonic boom occurs as the result of the piling up of compressional wavefronts along the conical edge of the wave pattern. These compressional wavefronts pile up and interfere to produce a very high-pressure zone. This is shown below. Instead of these compressional regions (high-pressure regions) reaching you one at a time in consecutive fashion, they all reach you at once. Since every compression is followed by a rarefaction, the high-pressure zone will be immediately followed by a low-pressure zone. This creates a very loud noise. If you are standing on the ground as the supersonic aircraft passes by, there will be a short time delay and then you will hear the boom - the sonic boom. This boom is merely a loud noise resulting from the high pressure sound followed by a low pressure sound. Do not be mistaken into thinking that this boom only happens the instant that the aircraft surpasses the speed of sound and that it is the signature that the aircraft just attained supersonic speed. Sonic booms are observed when any aircraft that is traveling faster than the speed of sound passes overhead.

It is not a sign that the aircraft just overcame the sound barrier, but rather a sign that the aircraft is traveling faster than sound. Doppler's effect - definition of Doppler's effect by The Free Dictionary Doppler's effect - definition of Doppler's effect by The Free Dictionary (dŏp′lər) n. A change in the observed frequency of a wave, as of sound or light, occurring when the source and observer are in motion relative to each other, with the frequency increasing when the source and observer approach each other and decreasing when they move apart. The motion of the source causes a real shift in frequency of the wave, while the motion of the observer produces only an apparent shift in frequency. Also called Doppler shift. [After Christian Andreas Doppler (1803-1853), Austrian physicist and mathematician who explained the phenomenon.] Doppler effect (ˈdɒplə) n (General Physics) a phenomenon, observed for sound waves and electromagnetic radiation, characterized by a change in the apparent frequency of a wave as a result of relative motion between the observer and the source. Also called: Doppler shift [C19: named after C. J.

Doppler (1803–53), Austrian physicist] Dop′pler effect` (ˈdɒp lər) n. a phenomenon characterized by a change (Dop′pler shift`) in the frequency of waves, as light or sound waves, observed when the wave source is moving relative to the observer. [1900–05; after C. J. Doppler (1803–53), Austrian physicist] Doppler effect As the source of sound waves (the ambulance) moves closer to the observer, the frequency of the sound waves and pitch of the sound become higher. As the source moves away from the observer, the frequency and pitch become lower. Dop·pler effect (dŏp′lər) The apparent change in the frequency of waves, as of sound or light, when the source of the waves is moving toward or away from an observer. Did You Know? When a car rushes past you on the road with the driver holding down the horn, you hear the horn change tone: it's higher pitched than normal as the car approaches and lower pitched as it departs. That's because of the Doppler effect. Sound waves spread outward in all directions from the horn.

The forward motion of the car compresses the sound waves traveling ahead of the car, making the wavelengths shorter. Sound having shorter wavelengths has higher frequency and therefore higher pitch—what you hear if the car is moving towards you. Behind the car, however, the sound waves are drawn apart. Longer wavelengths mean lower frequency and lower pitch, which is what you hear once the car rushes past. The Doppler effect works on light waves, too; in fact, this was how scientists determined that the universe is expanding. The light from galaxies and other distant celestial objects is shifted toward the red end of the spectrum (a phenomenon called red shift). Red light has the longest wavelengths of visible light. The pioneering astronomer Edwin Hubble reasoned that the red shift was due to the Doppler effect: the galaxies are speeding away from us, drawing out the wavelengths of the light emitted behind them, and the universe as a whole is expanding. doppler effect The phenomenon evidenced by the change in the observed frequency of a sound or radio wave caused by a time rate of change in the effective length of the path of travel between the source and the point of observation.

döppler effect Apparent change in the frequency of light waves or sound waves due to the relative motion of the observer and the source of the waves. ThesaurusAntonymsRelated WordsSynonymsLegend: Doppler Effect An apparent changing frequency of sound or - SCIENCE - 100 View Full Document Doppler Effect An apparent changing frequency of sound or light due to the relative motion of a source and an observer. Higher frequency Compressed sound waves for objects moving toward an observer. Lower Frequency Stretched out sound waves for objects moving away from an observer. The change in frequency can determine The speed the object is moving. This preview has intentionally blurred sections. Sign up to view the full version. View Full Document Red shift A shift in the wavelength to a longer wavelength determining that the galaxy is expanding. Suppose the light spectrum from a star shifted toward the blue end of the spectrum. What would this imply? The star is moving toward us. The doppler effect is used in what explantation of light? A change in frequency of light as the source moves relative to the observer. **Big Bang Theory The universe began with rapid expansion from a much more compact form. During the big bang what elements were formed within hours? Hydrogen and helium.

What three elements make up 90% of the human body? Hydrogen, oxygen, and carbon. What did gravity pull together to form galaxies from the big bang? Irregular clouds of gas and dust. Nuclear Fusion Very high temperatures and pressures in the interiors of stars fuses hydrogen atoms together to form helium. What causes gravity? Large masses. What causes stars to burn out? Decrease in hydrogen. Supernova Giant stars final stage of life cycle is a massive explosion. What are the principle components of the sun? Hydrogen and helium. Terrestrial planets Heavier, rock planets closer to the star. Jovian planets Lighter, gas-rich planets farther from the star. Heliosphere Space affected by solar wind. Solar wind a stream of charged particles from sun's magnetic field. What generates the northern lights? Interactions of solar wind with Earth's magnetic field. This is the end of the preview. Sign up to access the rest of the document. TERM Attacks the Scientist Instead of attacking the hypothesis or the data; science is not Review Notes Doppler Effect, What is the Doppler Effect? | Physics@TutorVista.com What is the Doppler Effect?

Doppler Effect is a wave phenomenon, it holds not only for sound waves but also for electromagnetic waves such as microwaves, radio waves and visible light. Doppler Effect can be defined as : The Apparent change in the frequency of sound when the source, the observer and the medium are in a relative motion is called Doppler Effect.For the waves which require a medium for their propagation, the apparent frequency depends on three factors : Velocity of the source Velocity of the medium or wind. For example, Let us consider an van moving with a siren and there are two observers, one which is moving towards the van and the other is moving away from the van. We could observe that the observer who is moving towards the van is experiencing High frequency and the observer who is moving away the van is experiencing low frequency. When a van blowing its whistle approaches him, the pitch of the whistle appears to rise and suddenly appears to drop as the van moves away from him. Doppler Effect takes place both in sound and light. If sound is considered, it is based on whether the source or observer or both are in motion, while if light is considered, it is based on the fact that whether the distance between the source and observer is decreasing or increasing.

Doppler Effect Sound In sound waves, there are some following conditions observed in Doppler effect. This effect depends upon whether the source is in motion or the observer. The velocity of medium affects the Apparent Frequency. Conditions observed in Doppler effect for sound waves: When the source of sound is in motion and the observer is at rest then the Doppler Effect is observed. When the observer is in motion and the source at rest then the Doppler Effect is observed. When the source and the observer are moving with unequal velocities then the Doppler Effect is observed. When the source and the observer and intervening medium are in motion then the Doppler Effect is observed. Limitations of Doppler effect in sound: The Velocity of source of sound must be less than that of the Velocity of sound i.e. Vs < V. The Velocity of observer must be less than the velocity of sound i.e. Vo< V. If the velocity of sound of source is greater than that of Velocity of sound then due to shock waves the wave front gets distorted, consequently the change in frequency will not be observed by the observer.

Conditions when Doppler Effect does not take place in Sound waves: When the source of sound and the observer both are at rest then the Doppler Effect in sound is not observed. When the source and the observer both are moving with the same velocity in same direction then the Doppler Effect is not observed. When the source and the observer are moving mutually in perpendicular directions then the Doppler Effect is not observed. When the medium only is moving then the Doppler Effect is not observed. When the distance between the source and the observer is constant then the Doppler Effect is not observed. Doppler Effect Light Back to Top The Velocity of light in free space is independent of the motion of source or observer and its universal constant given as, C = 3 $\times$ 108 m/sThus, the Doppler Effect in light depends only upon the relative motion of the light source and the observer and it does not matter which one is moving. When a light source and an observer are approaching each other with a velocity V, then the apparent frequency of light will be V’ = V V’ = V (1 – $\frac{v}{c}$) Here, V = Velocity of the body, c = Velocity of light.

which can be written as: V' - V = - V $\frac{v}{c}$ Let Apparent frequency is given by, V' - V = $\delta$ V Hence, the above equation can be written as: $\delta$ V = -V $\frac{V}{c}$ Case a: When the Light source is going away from the earth i.e., if Apparent frequency is less than real frequency then, V’ < V and $\delta$ $\lambda$ = lambda or $\lambda$‘ > $\lambda$ i.e. $\lambda$ is increased or spectral line will shift towards the red end of the spectrum. This is known as Red shift. Case b: When the light source is coming nearer to earth i.e., if Apparent frequency is greater than real frequency then, V’ > V and $\delta \lambda$ = - $\lambda$ Wavelength appears to be decreasing i.e. the spectral line in electromagnetic spectrum gets displaced towards violet end, Hence it is known as Violet shift. The Velocity of medium does not contribute to this effect frequency.

Doppler Effect Equation Apparent frequency is the frequency observed or heard by the observer when both Source and observer are moving: Some of the conditions and related formula of the Doppler Effect is mentioned below: (i) When both Source and observer moves towards each other : The Apparent frequency is given by n’ = n $\frac{v + v_{0}}{v – v_{s}}$ and Apparent wavelength $\lambda$' is $\lambda$’ = $\lambda$ $\frac{v – v_{s}}{v + v_{0}}$ Here, Apparent frequency is greater than Real frequency i.e., n’ > n and $\lambda$‘ < $\lambda$.

(ii) When both Source and observer move away from each other : The Apparent frequency is given by n’ = n $\frac{v – v_{0}}{v + v_{s}}$ then, Apparent wavelength $\lambda$' is $\lambda$’ = $\lambda$ $\frac{v + v_{s}}{v – v_{0}}$ Here, Apparent frequency is n’ < n and $\lambda$’ > $\lambda$ (iii) When the Source is approaching the Stationary observer : The Apparent frequency is given by: n’ = n $\frac{v – v_{o}}{v - v_{s}}$then Apparent wavelength $\lambda$' is $\lambda$’ = $\lambda$ $\frac{v - v_{s}}{v – v_{o}}$ (iv) When the Observer is approaching the Stationary source : The Apparent frequency is given by n’ = n $\frac{v + v_{o}}{v + v_{s}}$ then, Apparent wavelength $\lambda$' is $\lambda$’ = $\lambda$ $\frac{v + v_{s}}{v + v_{o}}$ (v) When Observer crosses the Source:

 Then Apparent frequency of source is given by n’ = n $\frac{v + v_{o}}{v}$ and Apparent frequency of observer n'' is n’’ = n $\frac{v + v_{o}}{v}$ $\delta$ n = n’ – n’’ = 2 n $\frac{v_{o}}{v}$ (vi) When moving source crosses a Observer : The Apparent frequency of source n' is given by n’ = n $\frac{v}{v + v_{o}}$and Apparent frequency n'' is n’’ = n $\frac{v}{v + v_{s}}$then $\delta$ n = 2 n $\frac{v_{s}}{v}$ Here, vs = Velocity of the Source, vo = Velocity of the Observer, v = Velocity of sound or light in medium, n = Real frequency, The above formulas are also called Doppler Formula.

Relativistic Doppler Effect Back to Top Relativistic Doppler Effect describes the changes of frequency of light wave when the source and observer are in relative motion. This can be explained using special theory of relativity. It is different from non relativistic Doppler Effect and includes the parameter of time dilation. The medium of propagation is not involved as a reference point. The Relativistic Doppler effect is given by T = $\frac{1}{1 – b}$ fsHere b = $\frac{v}{c}$ The velocity of observer as considered in terms of speed of light. Due to this time dilation, the time measured by the observer would be To = $\frac{t}{y}$ So, the Doppler shift is given as,y = $\frac{1}{\sqrt{1 – b^{2}}}$ Doppler Effect Simulation Back to Top Simulation is the imitation of the operation of a real world process or system over time. The basic goal in the simulation of the Doppler Effect is the simulation if the frequency shift caused by the source or observer. It can be simulated using java applet. Doppler Effect Example The Examples of Doppler effect are: Pitch is that feeling which produces a sensation of sound being sharp or thick.

The velocity of aeroplane in air. The apparent change in frequency n of the electromagnetic signal, sent from a rocket approaching the moon, being received by rocket driver reflected by moon is an example of Doppler Effect. Doppler Effect Problems These are the few problems on Doppler Effect in light and sound which are given below: Solved Example Question: A Submarine travels through water at a speed of 8.00 m/s, emitting a sonar wave at a frequency of 1400 Hz. The speed of sound in the water is 530 m/s. A second submarine is located such that both submarines are traveling directly towards each other. The second submarine is moving at 6.00 m/s. (A) What is the frequency detected by an observer riding on second submarine as the first submarine approaches it? (B) The submarine barely miss each other and pass. What frequency is detected by an observer riding on second submarine as the subs recede from it? (C) When both the submarine approaches each other, some of the sound from first submarine reflects from second submarine and returns to it. If the sound were to be detected by an first submarine, what is its frequency?

Solution: Wave-notes Wavelength The distance to where the wave repeats, (crest to crest or trough to trough). l meters (m) Amplitude The height of a wave measured from the center of the undisturbed material to the highest or lowest point of the wave (crest or trough). A meters (m) Crest The high point of a wave. Trough The low point of a wave Frequency The number of to and fro vibrations in a given time. For waves: The number of waves that pass in a given interval of time. f 1/s or Hertz (Hz) Period The time for a particular motion to repeat. For waves: The time for one complete wave to pass. T Wave speed The distance a wave travels divided by the time the wave travels. v Frequency and period are reciprocals of each other. f = 1/T or T = 1/f Period: The time for one complete wave to pass. symbol: T units: seconds (s) Frequency: The number of waves produced per unit of time. symbol: f units: 1/seconds or (Hz), (1/s) Frequency and period are reciprocals of each other.

f = 1/T and T = 1/f Same equation just rearranged. Wavelength: The distance from crest to crest. symbol: l units: meters (m) Wave speed: How fast a wave travels. The distance the wave travels divided by the time the wave travels. symbol: v units: meters/second (m/s) v = f*l Check the difference between wave speed and frequency! Types of Waves There are two types of waves that we will consider in this course, transverse and longitudinal. Transverse waves have the material that makes up the wave move at right angles to the direction of travel of the wave. Examples would be a guitar string or phone cord vibrating, or the crowd wave in a stadium (people stand then sit back down). Notice in the diagram below how the particle move up and down as the wave moves to the right. Longitudinal waves are those which move the particles that make up the wave parallel to the direction of travel of the wave. Examples would be sound waves and water waves under the surface.

In the diagram below, you can see how the particles move right and left as the wave moves to the right (particles move parallel to wave travel direction): Click here to see the differences between these two waves - along with examples of standing waves for each type. Water waves are a bit complicated, but generally the waves at the surface are thought of as transverse and the waves deeper down are longitudinal. They actaully are a combination of the two as particles move in ellipses. The deeper you go, the more longitudinal they become. Check out the diagram below: The Doppler Effect The Doppler Effect was first described by Christian Doppler (1803 - 1853) of Austria. The motion of a source of a wave or the motion of the receiver of the wave can affect the frequency of the wave. The best definition is as follows. The Doppler Effect is the apparent change in frequency of a wave due to the relative motion of the source or the receiver of the wave. All types of waves, sound, light, water, can exhibit the Doppler Effect. Example: A motorcycle moving toward you, the pitch is increased compared to when it is moving away from you. Why?

The speed of a wave in a material is constant. As you can see in this example, a source of waves which is stationary emits circular wavefronts in all directions. An observer to the right and left would observe the same wavelength and frequency. If the source moves to the right, you see the following: As the source or receiver moves toward each other the waves in front appear to squish together. A shorter wavelength means a higher frequency (bigger number). The product of wavelength and the wave frequency must equal the wave speed at all times. As the source or receiver move away from each other the opposite happens. The wavelength is longer which means the frequency must be lower (smaller number) in order for the wave speed to remain the same. In the picture above, you can see an observer to the right would observe a shorter wavelength, higher frequency. An observer to the left of this source would observe a longer wavelength, lower frequency. Applications of the Doppler Effect 1. Police use the Doppler Effect with radar waves to measure the speeds of cars. The radar compares the difference in the frequencies of the wave leaving the gun and the wave after reflecting off the speeding car. Yes, they can catch you coming or going.

The radars do not work as well when shot at an angle to the car. They work best head on or going directly away. 2. Doppler Shift of Visible Light A light source moving away from us would have a lower frequency (Red shift). A light source (such a galaxy) moving toward us would have a higher frequency (Blue shift). Astronomers have observed that all galaxies are moving away from the earth and have a slight red shift in the light coming to us. (Cool!) 3. Bow waves, shock waves and sonic booms If you have ever been in a boat, you have experienced the Doppler Effect with water. When you are traveling at a very slow speed in water the waves in front of the boat bunch together. As the boat moves faster the front begins to ride up on the constructive interference of the crests as they pile up on each other. When the speed of the boat equals the speed of the waves, there will be a very large amplitude wave built up in front of the boat called a WAVE BARRIER. see the diagram below: When the boat travels faster than the waves can move, a wake is created behind the boat. This is called a BOW WAVE.

The wake is a line of constructive interference making a large amplitude wave in the shape of a V behind the boat. Check it out below: Planes do the same thing in air when they fly faster than the speed of sound. The 3-dimensional cone shaped wake behind the plane has a special name. It is called a SHOCK WAVE. The shock wave is produced in the same manner as a wake. The air molecules squish together such that a region of high pressure is produced. Instead of two dimensions as with the boat the plane has a three dimensional wake (shock wave). When this compressed air passes by your ear it causes your eardrum to move violently inward. This violent motion is registered as a BOOM by your brain. Hence, the name sonic boom. There are actually two shock waves around planes, one at the leading edge and one at the trailing edge of the plane. Here is an F4 Phantom 30 feet off the runway going slightly faster than the speed of sound. Notice the two shock waves (one up front behind cockpit and one off the wings) in the cone shape.

These "clouds" are formed as the compressed air, which is just ahead of the cloud, returns to lower pressure condensing the water vapor onto particles in the air. This is why clouds form behind the wings of normal commercial jets as well. They are called con-trails (for condensation trails). If you have ever seen someone crack a whip you have experienced a shock wave in air. The tip of the whip is actually traveling faster that the speed of sound (about 700 mph). Neat. See the Doppler Effect in Action! To see this Doppler Effect in action, click here. It will open an applet in a separate window. You'll do an activity where you can change the speed of the moving object from slower than the wave speed to faster (so you can see the plane going faster than the speed of sound, etc.). You can also change the speed of the wave. This only demonstrates a moving wave source. This is a great visual of the Doppler Effect - check it out! Interference of Waves 1. The bending of waves through an opening is known as __diffraction_. 2. The two types of waves are _longitudinal_ and _transverse_. 3.

How do the particles in a particular medium move when a longitudinal wave passes through the medium? the particles in the medium vibrate parallel to the direction of motion of the wave. 4. How do the particles in a particular medium move when a transverse wave passes through the medium? the particles in the medium vibrate perpendicular to the direction of motion of the wave. 5. Sound is an example of a _longitudinal_ wave. 6. Although they are not true examples of this type of wave, the waves on the surface of water approximate _transverse_ waves. 7. The distance between two successive wave crests (or troughs) is called the _wavelength_ of the wave. 8. The height of a wave crest (or depth of trough) above the original undisturbed surface is called the _amplitude_ of the wave. 9. The number of waves that pass by a fixed point each second is defined as the _frequency_ of the wave and has units of _hertz_. 10. The symbol for wavelength is __l__ and __f_ for frequency. 11. The time between two successive wave crests is called the _period_ of the wave. 12.

When two or more waves meet at the same point, they add or subtract to form a new wave. This is known as the _principle of superposition_. (more than one word) 13. When two wave crests meet, they form a larger wave. This is an example of _constructive_ interference. 14. When a wave crest meets a wave trough, the resulting wave is a smaller wave. This is an example of __destructive__ interference. 15. The following picture shows two wave pulses on a string traveling toward each other at a constant speed. a. In the space below draw the resulting disturbance of the string when the two waves are on top of each other. a straight line should be drawn b. In the space below draw the resulting disturbance of the string after the two waves have passed each other. 16. Please label the following parts of the wave below. Wavelength, Crest, Trough, Amplitude 1. _wavelength_ 2. _amplitude_ 3. _crest_ 4. _trough_ 17. What is the diffraction of waves? The bending of waves as they move through an opening or around an obstacle.

The amount of diffraction is greatest when the opening or obstacle is much smaller that the wavelength. 18. Parallel water wave fronts are coming in towards two narrow openings (there is a wall between them on the other side so the waves can't interfere on the backside). In the diagram below, draw in the diffracted waves behind (to the right of) each opening to demonstrate the difference between the diffraction of the waves due to each opening. 19. Draw in the reflected wave fronts for the circular waves that are heading away from the focus of the reflector and towards the curved reflective surface below. Learner Goal 2 Please answer all questions in the space provided. Make sure that you show your work and include formulas and units. Please use the proper set up too. v=l·f v=l/T T=1/f 1. A water wave has a frequency of 2 Hz. and a wavelength of 0.5 meters. What is the wave speed of the water (in m/s)? Given: f = 2 Hz l = 0.5 m Want: v Eqn: v = l·f Solve: v = (2 Hz)(0.5m) = 1.0 m/s 2.

A light wave is traveling at 300,000,000 meters/second. If the wavelength of the light wave is 0.0000005 meters, what is the frequency of the light wave (in Hz)? Given: v = 3.0 x 10^8m/s l = 5.0 x 10^-7m Want: f Solve: f = (3.0 x 10^8m/s)/(5.0 x 10^-7m) f = 6.0 x 10^14 Hz 3. What is the period of the light wave in #2 above (in seconds)? Given: f = 1.5 x 10^14 Hz Eqn: T = 1/f Solve: T = 1/6.0 x 10^14 Hz T = 1.67 x 10^-15s 4. A middle C note (a sound wave) has a frequency of 256 Hz. If the speed of sound is 340 meters/sec., what is the wavelength of the middle C sound wave (in meters)?

Given: v = 340 m/s f = 256 Hz Want: l Solve: l = (340 m/s)/(256 Hz) l= 1.33 m 5. One of the FM radio stations listened to in our area is 94.5 FM. This means that the frequency of the radio waves is 94.5 million Hz or megahertz (MHz). If the radio waves travel at 300,000,000 meters/second, what is the wavelength of the radio wave (in meters)? Given: v = 3.0 x 10^8m/s f = 9.45 x 10^7Hz Want: l Solve: l= (3.0 x 10^8m/s)/(9.45 x 10^7Hz) l = 3.17 m Learner Goal 3 1. Draw pictures of bow waves for a boat traveling on water below the wave speed, at the wave speed and faster than the wave speed of the water. Pictures for this section can be found in your text book on pages 384-385. 2.

Whips , if cracked properly , are able to make small sonic booms near the end that is moving. Explain how this is possible. The tip of the whip is traveling at a speed greater than the speed of sound. when this happens small shock waves are produced at the tip of the whip. 3. The radar gun that police use to catch people speeding is based on the Doppler effect. In the space below explain how a radar gun works. If you need to draw a picture do so, make sure you write an explanation of what you drew. The radar gun works by sending out a radio wave of a set frequency. This wave bounces off the object being detected and changes frequency. The radar gun detects the frequency change and compares the outgoing frequency with the incoming frequency. The speed of the object is calculated based on the difference in frequencies. 4. Does the Doppler effect occur for only some types of waves or all types of waves? Explain. The Doppler effect is the apparent change in frequency of a wave due to the relative motion of the source of the wave or the receiver of the wave. All waves show this effect. 5.

Why is it that a subsonic aircraft, no matter how loud it may be, cannot produce a sonic boom? A subsonic aircraft cannot produce a sonic boom because of the fact that it needs to be traveling faster than the speed of sound in air in order for the shock wave to be developed.

Question: What is the word for the apparent change in frequency of a vibration due to the relative change in position of the observer?
Answer: Doppler effect