09.5 - Doppler Effect

Essential idea: The Doppler effect describes the phenomenon of wavelength/frequency shift when relative motion occurs.

Nature of science:

Technology: Although originally based on physical observations of the pitch of fast moving sources of sound, the Doppler effect has an important role in many different areas such as evidence for the expansion of the universe and generating images used in weather reports and in medicine. (5.5)

Understandings:

The Doppler effect for sound waves and light waves

Applications and skills:

Sketching and interpreting the Doppler effect when there is relative motion between source and observer
Describing situations where the Doppler effect can be utilized
Solving problems involving the change in frequency or wavelength observed due to the Doppler effect to determine the velocity of the source/observer

Guidance:

For electromagnetic waves, the approximate equation should be used for all calculations
Situations to be discussed should include the use of Doppler effect in radars and in medical physics, and its significance for the red-shift in the light spectra of receding galaxies

Data booklet reference:

v = velocity of wave

u_s = velocity of source

(Neg = source toward observer / Pos = source away from observer)

u_o = velocity of observer

(Pos = Observer towards source / Neg = Observer away from source)

International-mindedness:

Radar usage is affected by the Doppler effect and must be considered for applications using this technology

Theory of knowledge:

How important is sense perception in explaining scientific ideas such as the Doppler effect?

Utilization:

Astronomy relies on the analysis of the Doppler effect when dealing with fast moving objects (see Physics option D)

Aims:

Aim 2: the Doppler effect needs to be considered in various applications of technology that utilize wave theory
Aim 6: spectral data and images of receding galaxies are available from professional astronomical observatories for analysis
Aim 7: computer simulations of the Doppler effect allow students to visualize complex and mostly unobservable situations

Doppler Effect - Ultrasound

Physical principles of Doppler ultrasoundVisit the post for more.

Doppler Radar Weather Forcasting

In the image above, the grey line is the transmitted signal. You can see how the returned energy changes its wavelength characteristics when it hits a target moving away or toward the radar (red and green line, respectively)

Bird Roost Rings. These are most common in the fall around bodies of water that typically have temperatures warmer than the surrounding land at night. It is also the time birds are gathering for the seasonal migration. At night, birds rest/nest in and around the lakes. Just before sunrise, there is often a coordinated lift off and dispersion of the birds out into the surrounding fields for feeding during the day. My hometown is in the bottom center of the image in Ogle County.

Dual-polarization revolutionized radar technology by providing better resolution and a clearer view of storms and corresponding storm structure which is critical for real-time forecasting and research purposes. Dual-polarized radars send both horizontal and vertical electromagnetic waves to examine a variety of particle, hydrometeor, and/or biological target types existing within different types of air masses. These perpendicular fields bounce off of an object and return back to the radar which then gives information on the horizontal and vertical dimensions of particles, hydrometeors, and/or biological targets within the observable range of a given radar site. Dual-polarized radar technology is important because it can accurately predict the amount of potential rainfall. Also, it can differentiate between heavy rain and hail, which can improve the efficiency and accuracy of flash flood watch and/or warning issuance.

Doppler Shift in Astronomy

Moving Sources and Sonic Booms

Doppler Effect Data Analysis.pdf

Doppler Simulations / Visualizations

Doppler Effect Bkgnd Info

A variation in the perceived sound frequency due to the motion of the source is an example of the Doppler effect. The Austrian physicist Christian Doppler (1803–1853) first described this effect.

Doppler Effect MCQs - Paper 1

Sound of a constant frequency f0 is being emitted by a sound source. An observer O travels in the direction shown at a speed of 0.1 v where v is the speed of sound.

Which of the following gives the relationship between f0 and the frequency f of observed sound? C.

a. f = 1.1f0 c. f0 < f < 1.1f0

b. f = 0.9f0 d. f0 > f > 0.9f0

3. A source S, moving at constant speed, emits a sound of constant frequency. The source passes by a stationary observer O, as shown below.

Which one of the following shows the variation with time t of the frequency f observed at O as the source S approaches and passes by the observer. C.

2. Which one of the following diagrams best represents wavefronts produced by a source of sound of constant frequency as it moves at constant speed towards a stationary observer at O? A.

Doppler Effect Problems

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 on this day is 345 m/s. 877.7 Hz (b) What frequency does she receive after the ambulance has passed? 734.9 Hz

A spectator at a parade receives an 888-Hz tone from an oncoming trumpeter who is playing an 880-Hz note. At what speed is the musician approaching if the speed of sound is 338 m/s? 33.5 m/s

A commuter train blows its 200-Hz horn as it approaches a crossing. The speed of sound is 335 m/s. (a) An observer waiting at the crossing receives a frequency of 208 Hz. What is the speed of the train? 12.9 m/s (b) What frequency does the observer receive as the train moves away? 192.6 Hz

How fast, in kilometers per hour, must an observer be moving toward a source to make the observed frequency 5% greater than the true frequency? (Assume that the speed of sound is 340m/s.) u_o = 17m/s

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 sound in air to be 343m/s .) 28.1 m/s

Doppler Effect Problem Sets

Doppler Effect TSPs

Doppler Effect Problems IB.pdf