Explore BrainMass

Doppler Shift

The Doppler effect is the change in frequency of a wave for an observer moving relative to its source. It is most commonly observed in everyday life by the sounding of a siren or horn that approaches, passes and goes away from an observer. The received frequency is higher, compared to the emitted frequency during the approach, is identical at the instant of passing and is low during the recession.

The relative change in frequency can be explained by the source of the wave changing positions. When the waves are travelling, the distance between successive wave fronts is reduced so that waves are “bunched together”. Conversely, if the source of waves is moving away from the observer, each wave is emitted further from the previous. The distance between successive wave fronts is increased and “spread out”.
In classical physics, the speed of the source and the receiver relative to the medium are lower than the velocity of waves in the medium. The observed frequency has a relationship to the emitted frequency given by:

f=( (c+ v_r)/(c+v_s ))f_0

Where c is the velocity of waves in the medium, vr is the velocity of the receiver relative to the medium and vs is the velocity of the source relative to the medium. The change of frequency can be found from the equation:

∆f= ∆v/c f_0


∆f=f- f_0

∆v= v_r- v_s

If the moving source is emitting waves with an actual frequency f0, then an observer stationary relative to the medium detects waves with a frequency f given by:

f=(c/(c+ v_s )) f_0

A similar analysis for a mover observer and a stationary source has the observed frequency:

f=((c+ v_r)/c) f_0

Categories within Doppler Shift

Twin Paradox

Postings: 3

The twin paradox is a thought experiment in special relativity involving identical twins.

The beat detected on a moving platform

A speaker fixed to a moving platform moves to a wall, emitting a steady sound with a frequency of 250Hz. A person on the platform, right next to the speaker detects the sound waves reflected off the wall, and those emitted by the speaker. How fast should the platform move, vp, for the person to detect a beat frequency of 4.0

Properties of sound waves

1. Sound waves travel through an aluminum bar at a speed of 1400 m/s. If the frequency of the sound wave is 880 Hz, what is the distance between crests on a sound wave traveling through aluminum? 2. An airplane flies horizontally at a constant speed, piloted by rescuers who are searching for a disabled boat. When the plane

Bystander hears a siren; open organ pipe frequencies

1. A bystander hears a siren vary in frequency from 476 Hz to 404 Hz as a fire truck approaches, passes by, and moves away on a straight street. What is the speed of the truck? (Take the speed of the sound in air to be 343 m/s) 2. An open organ pipe is 0.50 m long. If the speed of the sound is 340 m/s, what are the pipe's fun


Please show work 1. In your own words, explain the meaning of the following terms: a. Traverse waves b. Longitudinal waves c. Standing waves d. Shock waves 2. Police use Doppler radar to detect speeding cars. Explain how the Doppler effect is used in this application. 3. A person in a cave emits a sound and rece

Physics waves- frequencies: two submarines underwater approach each other

Two submarines are underwater and approaching each other head-on. Sub A has a speed of 13 m/s and sub B has a speed of 7 m/s. Sub A sends out a 1150 Hz sonar wave that travels at a speed of 1522 m/s. (a) What is the frequency of the sound detected by sub B? ______Hz (b) Part of the sonar wave is reflected from B and retu

Doppler's Effect: Apparent change in frequency

Please see the attachment. I have a test today and this question was on my old test . but I want to know how to solve other scenarios like this. ( I made up some questions below ) A stationary observer hears a frequency of 500Hz while the source is moving directly toward him. If he hears a frequency of 400Hz when the sourc

Doppler Shift Lab

At-Home Experiment 1 PURPOSE This experiment was designed to understand and measure Doppler shift. Equipment Setup Tuning fork (with a known frequency) Nylon string Stopwatch Meter Stick Tie the string (1 meter long) to the end of the tuning fork. Procedure First, practice swinging the tuning fork in a horizonta

Velocity transformation/relativistic doppler effect

The Starship Enterprise approaches a planet at a speed of 0.8 c. The planet is considered at rest. A Klingon fighter ship approaches from the opposite direction at 0.6 c. (a) What speeds do people at each location see the other traveling? (b) A light signal of 100 MHz is issued by Enterprise. What speed does each measure


Show ALL your work, including the equations used to solve the problems. A French submarine and a U.S. submarine move toward each other during maneuvers in motionless water in the North Atlantic. The French sub moves at 50.0 km/h, and the U.S. sub at 70.0 km/h. The French sub sends out a sonar signal (sound wave in water) at

Doppler Effect Problems

1. One end of stationary rope is tied to a support at the end of a vertical mine shaft 800m deep, the other end is fixed at the bottom by means of a 20kg weight. If a man at the bottom of the shaft signals to someone at the top by jerking the rope sideways, how long will it take for this signal to travel from bottom to top of th

Doppler effect: Sound source, frequency, speed of sound

A sound source and a person are separated by 1000m. The sound source produces a frequency of 400Hz. Given speed of sound in air @ 343 m/s find: 1) Source moves toward person at 20 m/s, what frequency does the person hear? 2) If source stays still, but the person moves toward the sound source at 20 m/s, what frequency wil

Physic Questions about Sound and Dopplers Effect

Question 1: Particles approximately 3.0 X 10-2 cm in diameter are to be scrubbed loose from machine parts in an aqueous ultrasonic cleaning bath. Above what frequency should the bath be operated to produce wavelengths of this size and smaller? Helpful tip. The speed of sound (s) is equal to the frequency (f) times the wavelengt

Two problems on Doppler effect of sound

(See attached file for full problem description) --- 20.36 An opera singer in a convertible sings a note at 600 Hz while cruising down the highway at 90 km/hr. Part A : What is the frequency heard by a person standing beside the road in front of the car? Part B : What is the frequency heard by a person on the gro

Physics: Sonar and Frequency

1. A sonar signal from a "fish finder" in fresh water returns 0.0460 seconds after being transmitted. What is the distance to the fish that reflected the sound? 2. (a) What frequency is received by a person watching an oncoming ambulance moving at 110 km/h and emitting a steady 800 Hz sound from its siren? The speed of sound


A siren is mounted on a tower and emits a sound whose frequency is 2140 Hz. A person is driving a car awayf rom the tower at 27 m/s. The sound reaches the person by 2 paths: the sound reflected from a buliding in the front of the car and the sound coming directly from the siren. The speed of sound is 343 m/s. What frequency d

Doppler effect

The predominant frequency of a certain police car's siren is 1550Hz when at rest. What frequency do you detect if you move with a speed of 30.0m/s (a) toward the car, and (b) away from the car?

Range Difference and Radar Problem

Part a of the problem - word document - requires determination of the range at point C and P then determining the difference. I'm unsure if I need to concern myself with the Taylor series expansion of the range equation. In essence I opted to determine theta then solve for R using the range equation (right before the Taylor

The Doppler Effect

A source of sound waves of frequency 1.0 kHz is stationary. An observer is traveling at 0.50 times the speed of sound. What is the observed frequency if the observer moves toward the source? What is the observed frequency if the observer moves away from the source instead?

Find the frequency of Sue's scream in the cave and calculate distance to the pool

John and Sue are descending on ropes into a cave. Sue's rope breaks and she falls screaming past John. Apply doppler effect. John, hanging stationary on a rope in an underground cave, hears Sue screaming with frequency f as she falls past him with constant terminal speed S= 53 m/sec. While she is above him, he receives her sc

Sound frequency and/or wavelength changes due to motion of the observer

A truck is moving at 50 m/sec while its horn emits a steady note at 280 cy/sec. A woman is stationary, 150 meters ahead of the truck. A man is in a car, 200 meters ahead of the truck, moving toward the truck at a speed of 30 m/sec. The speed of the sound is 345 m/sec. PART a. Find the frequency heard by the woman. PART b.

Velocity, frequency of sound

1.A supersonic jet traveling at Mach 3 at an altitude of 20000m is directly overhead at time t=0. A) How long will it be before the ground observer encounters the shock wave? B)Where will the plane be when it is finally heard?(Assume an average value of 330m/s for speed of sound in air) I will send what I have for this one

Calculating sound waves, wavelength shift in regards to the Doppler Effect.

A sound detector is placed on a railway platform. A train, approaching the platform at a speed of 36km/h sounds its whistle. The detector detects 12 kHz as the most dominant frequency in the whistle. If the train stops at the platform and sounds the whistle, what would be the most dominant frequency detected? The speed of sound

Sound Waves

The ear has a protective overload mechanism called the "acoustic reflex". A sound in excess of about 85 dB causes muscles attached to the eardrum and ossicles to engage, which provides a safety margin of about 20 dB or 30 dB (the equivalent of ear plugs). This reflex takes about 30 ms to 40 ms to cut in, and maximum effect only