IB Physics HL C.5 Doppler Effect Question Bank

Practise IB Physics HL C.5 by solving Doppler-shift problems and interpreting moving-source, observer and wave-medium evidence.

Exam points

Apply Doppler equations for moving sources and observers with explicit direction and sign conventions.
Relate frequency shifts to velocity measurements and distinguish classical from relativistic limits in data.
Evaluate spectra, uncertainty and model assumptions when inferring motion from observed frequency.

Covered syllabus points

C.5.1—Doppler effect C.5.2—Doppler wavefront diagrams C.5.3—Light Doppler approximation C.5.4—Spectral line shifts C.5.5 (HL)—Mechanical-wave Doppler formulas

[Maximum number: 4]

Two loudspeakers, A and B, are driven in phase and with the same amplitude at a frequency of 850 Hz . Point P is located 22.5 m from A and 24.3 m from B. The speed of sound is $340 \mathrm{~ms}^{-1}$ .

Figure for Question C.5 Doppler effect question 1 — IB Physics HL

(a)

In another experiment, loudspeaker A is stationary and emits sound with a frequency of 850 Hz . The microphone is moving directly away from the loudspeaker with a constant speed v. The frequency of sound recorded by the microphone is 845 Hz .

[ 4 ]

(i)

Explain why the frequency recorded by the microphone is lower than the frequency emitted by the loudspeaker.

[ 2 ]

(ii)

Calculate v.

[ 2 ]

$\begin{aligned} 845=850 \times \frac{340-v}{340} v=2.00<\mathrm{m} \mathrm{~s}^{-1}>- \end{aligned}$

[Maximum number: 1]

A point source of sound is moving to the right at constant speed. The source emits sound waves of constant frequency. The speed of the source is less than the speed of sound. Which diagram correctly shows the wavefronts of the sound?

Figure for Question C.5 Doppler effect question 2 — IB Physics HL — Option A

Figure for Question C.5 Doppler effect question 2 — IB Physics HL — Option B

Figure for Question C.5 Doppler effect question 2 — IB Physics HL — Option C

Figure for Question C.5 Doppler effect question 2 — IB Physics HL — Option D

[Maximum number: 4]

Star A is a main sequence star.

The data for Star A and the Sun are given in a table.

Table for Question C.5 Doppler effect question 3 — IB Physics HL

(a)

The peak wavelength of the radiation from Star A is measured by an observer on Earth. The observed wavelength is 0.007 % less than the value in (c)(i).

Outline how this difference arises.

[ 2 ]

(b)

Determine the speed, in $\mathrm{km} \mathrm{s}^{-1}$ , of Star A relative to Earth.

[ 2 ]

$\begin{aligned} v=\frac{\Delta \lambda}{\lambda} c=\frac{0.007}{100} \times 3 \times 10^{8}=21000 21 \mathrm{~km} \mathrm{~s}^{-1} \end{aligned}$

Allow ECF for MP2.

Do not award MP1 for use of the Doppler formulas for sound and mechanical waves.

All question bank results loaded

Covered syllabus points

C.5 Doppler effect question 1

Question (a)

Question (i)

Question (ii)

C.5 Doppler effect question 2

C.5 Doppler effect question 3

Question (a)

Question (b)