What is Doppler effect: Definition and 505 Discussions
The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who described the phenomenon in 1842.
A common example of Doppler shift is the change of pitch heard when a vehicle sounding a horn approaches and recedes from an observer. Compared to the emitted frequency, the received frequency is higher during the approach, identical at the instant of passing by, and lower during the recession.The reason for the Doppler effect is that when the source of the waves is moving towards the observer, each successive wave crest is emitted from a position closer to the observer than the crest of the previous wave. Therefore, each wave takes slightly less time to reach the observer than the previous wave. Hence, the time between the arrivals of successive wave crests at the observer is reduced, causing an increase in the frequency. While they are traveling, the distance between successive wave fronts is reduced, so the waves "bunch together". Conversely, if the source of waves is moving away from the observer, each wave is emitted from a position farther from the observer than the previous wave, so the arrival time between successive waves is increased, reducing the frequency. The distance between successive wave fronts is then increased, so the waves "spread out".
For waves that propagate in a medium, such as sound waves, the velocity of the observer and of the source are relative to the medium in which the waves are transmitted. The total Doppler effect may therefore result from motion of the source, motion of the observer, or motion of the medium. Each of these effects is analyzed separately. For waves which do not require a medium, such as electromagnetic waves or gravitational waves, only the relative difference in velocity between the observer and the source needs to be considered, giving rise to the relativistic Doppler effect.
I have a problem in regard to the doppler effect,which may be generalised to all waves--sound,water etc.
Please explain why the observed frequency increases as the object approaches an observer and then decreases as the object passes the observer.Actually,I thought that since doppler effect...
Hi, I've got a problem that I can't seem to find an explanation to, about the Doppler Effect
An ambulance is going down the road at a speed U meters/second, in the same direction as the wind, which has a speed of W meters/second. The speed of sound in air is c meters/second
Now, I have to...
Homework Statement
A loud speaker is connected to a string (spring constant k = N/m). The speaker moves back and forward in simple harmonic motion with an Amplitude of 0.8m. The frequency of an oscillation for amass on a string is w = (k/m)^1/2. The mass of the speaker is 90.0g.
What is...
Homework Statement
A bat flies toward a wall, emitting a steady sound with a frequency of 25.0 kHz. This bat hears its own sound plus the sound reflected by the wall.
How fast should the bat fly, v_b, to hear a beat frequency of 220 Hz?
Take the speed of sound to be 344 m/s...
Hi, I'm new to these forums. I just had a question about the Doppler effect on light (red and blue shifts of light). I've read how it is supposed to work, but I also read in a book that the speed of light is constant in all moving frames.
So if you've got a galaxy moving towards you, and...
Doppler Effect- Observer On Angle To Source
Plz help- I've been working on this for 2 days and I'm down to my last teaspoon of coffee powder. Even having the answer didn't help!
I think sleepness is turning me into a zombie :eek: ...prehaps eating brains will help me solve this problem...
Homework Statement
Standing in line next to the scariest rollercoaster of all time, you see your friends screaming their heads off as they come speeding out of the end of the ride. The sound of their screams is about 30% higher in pitch than normal due to the Doppler shift caused by their...
Homework Statement
source emits sound with a characteristic frequency of 640 Hz. Calculate the observed frequency and the wavelength between source and observer in each of the following situations.
a) The observer approaches a stationary source at 57 m/s
b) Both the source and observer move...
Homework Statement
A whistle of frequency 500 Hz tied to the end of a string of length 1.2 m revolves at 400 rev/min. A listener standing some distance away in the plane of rotation hears frequencies in the range ____?
(speed of sound=340 m/s)
a) 436 to 586
b) 426 to 574
c) 426 to 584
d)...
Homework Statement
A boy is walking away from a wall towards an observer at a speed of 1 m/s and blows a whistle whose frequency is 680 Hz. THe number of beats heard by the observer is ____.
(Velocity of sound in air=340 m/s)
a) zero
b)2
c)8
d)4
Homework Equations
The Attempt at...
Homework Statement
An object producing a sound with frequency 500 Hz is traveling at 40 m/s toward an observer, and the observer is traveling at 30 m/s away from the source. Another source producing a sound with the same frequency is traveling at 10 m/s toward a stationary observer...
How to prove the doppler effect for light wave?
Isn't that the speed of light is constant for both the observer and source?
If the wavelength for both the source and observer is the same, then the frequency is the same too, so there is no doppler effect?
If the wavelength is different...
Astronomers believe that the universe is expanding because of the measured doppler effect redshift of light emitted from distant stars in other galaxies, correct? Do they have other reasons for believing that the universe is expanding? The stars in our own galaxy are known to not be traveling...
"Basic" problem regarding doppler effect of light (E/M waves)
1. At what speed would one have to move at to see a red light as green. Presume red light wavelength = 630nm and green light wavelength = 530nm.
2. f0=fs√([1+v/c]/[1-v/c])
>f0 = observed frequency
>fs = source frequency
>v...
what does the doppler effect mean for an individual photon? for instance in a blue shift do the photons actually have more energy if they were originally a lower frequency?
I remember reading in a book that if we approached a red light
really fast it would appear green to us due to the Doppler effect of light
does anyone know how fast we would need to travel for this to happen.
Homework Statement
A car is driving down the road at 25m/s. Inside the car, the radio is blaring music at 1800Hz. How would it sound to a person standing still a) in front of the car b) behind the car?Homework Equations
[fo/(vw+vo)] = [fs/(vw-vs)]The Attempt at a Solution
a)
[fo/(vw+vo)] =...
Homework Statement
A radar beam has a wavelength of .02 m. The frequency is 17500 Hz. What would be its echo frequency if a rocket 60km away is moving at 500m/s and the radar is coming from a jet moving at 310m/s towards the rocket which is aimed at it? (b) Would the rocket appear red shifted...
Homework Statement
A train approaches, and passes through, a station. During this period the velocity of the train is constant and the engine is continuously sounding its whistle. Which one of the following correctly describes what an oberver on the platform will hear?
Sound heard as...
Homework Statement
An ambulance with a siren emitting a whine at 1530 Hz overtakes and passes a cyclist pedaling a bike at 2.22 m/s. After being passed, the cyclist hears a frequency of 1519 Hz. How fast is the ambulance moving? (Take the speed of sound in air to be 343 m/s.)
Homework...
Homework Statement
Hearing the siren of an approaching fire truck, you pull over to the side of the road and stop. As the truck approaches, you hear a tone of 470 Hz; as the truck recedes, you hear a tone of 400 Hz. How much time will it take the truck to get to the fire 2.5 km away assuming...
Homework Statement
A car moving at 35 m/s approaches a stationary whistle that emits a 220 Hz sound. The speed of sound is 343 m/s. What is the speed of sound relative to the driver of the car?
Homework Equations
fo = fs [1 +/- vo/v] / [1 +/- vs/v]
The Attempt at a Solution
Dont...
Homework Statement
Horseshoe bats use the Doppler Effect to determine their
location. A horseshoe bat flies toward a wall at a speed of 15 m/s while emitting a sound of
frequency 35 kHz. What is the beat frequency between the emission frequency and the
echo? Assume that the air temperature is...
If I could please get some help on these really puzzling questions, that would be great.
Consider these formulas:
If a light source with frequency fo is moving away at speed v, then you see the frequency to be lower according to
f=fo( (the square root of 1-(v/c)) / (the square root of...
I recall being taught that electrons in various "orbitals" or "energy states" absorb and emit photons of a specific frequency. I also learned that relative speed changes the observed wavelength of photons, due to the Doppler Effect.
So, how is it that some electron can "absorb" a photon of a...
At a distance of 20m from a source of sound, the sound level is 40dB. If the observer backs up to a distance of 40m from the source, what will the sound level be?
Basically, I said that the sound level halved = 20dB. Correct?
You are standing on railroad tracks as a train approaches at a constant velocity. Suddenly the engineer sees you, applies the brakes, and sounds the whistle. What do you hear starting at that moment?
Because the waves are "stretching" as it approaches you slower and slower, I said that the...
Homework Statement
Ok here's the problem.. a little lengthy so bear with me :) (3 parts need help w/ last two)
Expectant parents are thrilled to hear their unborn baby's heartbeat, revealed by an ultrasonic motion detector. Suppose the fetus's ventricular wall moves in simple harmonic...
Homework Statement
A Doppler blood flow unit emits ultrasound at 5.0 {\rm MHz}.
What is the frequency shift of the ultrasound reflected from blood moving in an artery at a speed of 0.20 m/s?
What equations would I use to calculate the doppler shift? It is not in my textbook...
1. Homework Statement
At the Winter Olympics, an athlete rides her luge down the track while a bell just above the wall of the chute rings continuously. When her sled passes the bell, she hears the frequency of the bell fall by the musical interval called a minor third. That is, the...
I know which equations to use for solving Doppler Effect problems, so figuring out which is the observer and which is the source and which is moving or stationary is not the problem, the problem I am having is in solving the actual formulas... This question might belong in the math help section...
1. http://www.prep101.com/MCAT/102MCATPhysicsAnswers.pdf number 15
2. As you can see I already have the answers, I think I'm just doing something wrong.
3. I already know that the answer will be 'away' making it either a or c. So first I plugged the equation given (f1 =...
Homework Statement
The security alarm on a parked car goes off and produces a frequency of 735 Hz. The speed of sound is 343 m/s. As you drive toward this parked car, pass it, and drive away, you observe the frequency to change by 78.4 Hz. At what speed are you driving?
2. The attempt at...
Homework Statement
Suppose a heart's ventricular wall moves in simple harmonic motion with amplitude 1.8mm and a frequency of 115 per minute. (a) Given a motion detector in contact with the chest produces sound at 2,000,000Hz which travels through tissue at 1.50 km/s. Find the maximum linear...
John is listening to a horn. He knows the frequency of the horn is 300 Hz when both he and the horn are at rest. If he hears a pitch of 330 Hz, there are clearly several possibilities. (Give ALL correct answers, i.e., B, AC, BCD...)
A) Both can be moving and have the same speed.
B) Both can...
I do not fully understand the Doppler effect in light.
A theoretical question:
If I was traveling near the speed of light, towards a source of light. Would all the wavelengths in the visible spectrum be shortened and therefor, everything shifting towards red?
I thought the speed of...
Homework Statement
Do not attempt to do this experiment! You are sitting on railroad tracks,
and extremely fast trains are approaching from both the left and the right.
These trains have equal speeds, and both send out a warning signal with their
horns. You hear this signal at a frequency...
Homework Statement
Two adjacent sources each emit frequency 800 hz in air (340 m/s). how far would source 1 have to be moved so an observer in front of the sources would hear no sound? .321 .213 .123 or .312.
Homework Equations
f' = f/(1+ vsource/vsnd)
The Attempt at a Solution
i...
Homework Statement
Hydrogen's only visible spectral lines are 656, 486, 434, and 410 nm. If spectral lines were of absolutely precise wavelength, they would be very difficult to discern. Fortunately, two factors broaden them: the uncertainty principle and the doppler broadening.
Atoms in...
Homework Statement
Assuming the speed of sound is 338 m/s:
A bat moving at 6.2 m/s is chasing a flying insect. The bat emits a 53 KHz chirp and receives an echo at 53.6 KHz. At what speed is the bat catching up on its prey?
Homework Equations
f^{'}=[ (V_{Air} + V_{observer}) /...
Homework Statement
Speed of sound in air is 340m/s. Sound from a jet, moving a 100m/s through the air, will have a speed of:
Homework Equations
Doppler effect, and v = Sqrt(bulk/density)
The Attempt at a Solution
The answer for this is 340m/s. I was wondering why. Because all the...
Homework Statement
A source of sound mvoes along one straight line between listeners Abigail and Bertha. The wavelength of the sound waves heard by Abigail is about 1/2 the wavelength heard by Bertha. What is the ratio of of the speed of the source to the speed of sound? Assume that the air...
Homework Statement
The calibration for a piece of ultrasound equipment states that the velocity of blood flow in the aorta is normally about 0.28 m/s, and that the detector emits a frequency of 4.20 MHz.
a) If the ultrasound waves were directed along the blood flow and reflected from the...
Homework Statement
A source of 1-kilohertz sound is moving straight toward you at a speed .9 times the speed of sound. The frequency you receive is:
Homework Equations
\nu = \frac{v}{\lambda}
f' = \frac{v + v'}{v} f
The Attempt at a Solution
When I attempt the...
[SOLVED] Doppler Effect?
Homework Statement
A bat flying at 4.0 m/s emits a chirp at 20 kHz. If this sound pulse is reflected by a wall, what is the frequency of the echo received by the bat?
Homework Equations
Not sure. Do I use the f(1)=f*[(v+/-observer velocity)/(v+/-source...
I'm trying to detect a remote moving target. I know that if I send out a light beam against a distant target that is moving towards or away from me that the reflected light will be frequency shifted by a small amount. Now what if I amplitude modulated the light with an audio frequency. Would...
[SOLVED] Relativistic Doppler Effect and a Baseball
Homework Statement
A baseball coach uses a radar device to measure the speed of an approaching pitched baseball. This device sends out electromagnetic waves with frequency f_0 and then measures the shift in frequency \Delta f of the...
Homework Statement
Two trumpet players tune their instruments to exactly 440 Hz. Find the difference in the apparent frequencies due to the Doppler effect if one plays her instrument while marching away from an observer and the other plays while marching toward the observer. Is this enough to...
When a police car passes you with a siren with a frequency of 440 Hz, a noticeable
drop in the pitch of the sound of the siren will be observed as the car passes by. But why the pitch suddenly drops when the car is passes by?
I am not pretty sure why I heard the pitch suddenly drops, but I...