IBPhysicsSLExam QuestionsWave BehaviourDoppler Effect

Syllabus Edition

First teaching 2023

First exams 2025

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Doppler Effect (SL IB Physics)

Exam Questions

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Doppler Effect

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Doppler Effect

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1
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A train is moving towards a stationary observer. The train sounds its horn. 

What are the correct changes in frequency, wavelength and pitch of the horn as heard by the observer?

 

Frequency

Wavelength

Pitch

A.

 higher shorter higher

B.

 higher shorter lower

C.

 lower shorter lower

D.

 lower longer higher

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    2
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    Which diagram correctly represents redshift?

    • MOXMBiNh_9-5-ib-hl-mcqs-easy-q4-answer-a

    • QT2IILu6_9-5-ib-hl-mcqs-easy-q4-answer-b

    • cT1iN0fM_9-5-ib-hl-mcqs-easy-q4-answer-c

    • QLm3_b0~_9-5-ib-hl-mcqs-easy-q4-answer-d

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    3
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    What did the discovery of the Doppler redshift give scientists evidence for? 

    • Newton's Third Law

    • The formation of solar systems

    • The Big Bang

    • Blueshift

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    4
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    Which of the following is not a use of the Doppler effect?

    • Mapping the expansion of the universe

    • Measuring the rate of blood flow in patients

    • Finding planetary orbits around distant stars

    • Recording the speed of sound 

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    5
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    Which statement about redshift is true?

    • Redshift shows all galaxies are moving towards the Earth

    • Redshift shows that the space between galaxies is expanding

    • Redshift is the change in pitch of the sound waves emitted from galaxies

    • Redshift is the expansion of stars

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    6
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    Which of the following statements about the Doppler effect is correct?

    • When a galaxy moves towards the Earth the spectral absorption lines observed will have a longer wavelength

    • When a car starts to move away from an observer, the sound from the exhaust appears at a lower frequency to the observer than the driver

    • When a train moves towards a station, it's horn will sound lower to the passengers on the platform compared to the passengers in the train

    • Light from a star moving towards the Earth is redshifted

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    7
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    Which of the following is an equation to calculate the Doppler shift of light?

    • fraction numerator capital delta f over denominator f end fraction almost equal to c over v

    • fraction numerator f over denominator straight capital delta f end fraction almost equal to v over c

    • v over f almost equal to fraction numerator c over denominator straight capital delta f end fraction

    • fraction numerator capital delta f over denominator f end fraction almost equal to v over c

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    1
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    In the laboratory on Earth, hydrogen emits a spectral line that is measured by an observer to have a wavelength of 400 nm. The same spectral line is emitted by a galactic source that is moving away from Earth at speed of 0.2c, where c is the speed of light.

    What is the wavelength of the same spectral line from the galaxy as measured by the observer on Earth?

    • 480 nm

    • 320 nm

    • 80 nm

    • 2000 nm

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    2
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    A spectral line is observed at 530 nm in the laboratory. The same spectral line is observed in a galaxy which is receding from Earth at a velocity of 3.00 × 106 m s−1. 

    What is the wavelength of the spectral line from the galaxy?

    • 534.7 nm

    • 5.3 nm

    • 535.3 nm

    • 583 nm

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    3
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    A star emits light of frequency f. This light is observed on Earth to have a frequency f to the power of space apostrophe end exponent which is of a lower frequency than f.

    Which of the following correctly describes the speed and direction of motion of the star?

      Speed Direction
    A. fraction numerator left parenthesis f minus f space apostrophe right parenthesis over denominator f end fraction c Towards Earth
    B. fraction numerator left parenthesis f minus f space apostrophe right parenthesis over denominator f space apostrophe end fraction c Towards Earth
    C. fraction numerator left parenthesis f minus f space apostrophe right parenthesis over denominator f end fraction c Away from Earth
    D. fraction numerator left parenthesis f minus f space apostrophe right parenthesis over denominator f space apostrophe end fraction c Away from Earth

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      4
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      Two lines P and Q in the emission spectrum of a gas are measured on the Earth by a stationary observer.

      9-5-doppler-hl-mcqs-medium-q8-question

      The observer then moves towards the gas sample, and the emission spectrum is recorded as they are moving.

      What is the correct pattern for the shifted spectral lines, P' and Q'?

      • 9-5-doppler-hl-mcqs-medium-q8-answer-a

      • 9-5-doppler-hl-mcqs-medium-q8-answer-b

      • 9-5-doppler-hl-mcqs-medium-q8-answer-c

      • 9-5-doppler-hl-mcqs-medium-q8-answer-d

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      5
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      Which of the following statements is true about redshift?

      • Redshift led to the idea that galaxies are expanding

      • A greater redshift means a faster speed of recession

      • Redshift shows a few of the galaxies in the universe are moving away from a single point

      • Redshift causes electromagnetic waves to change frequency and speed.

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      1
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      An alien living in another solar system sends a radio signal of frequency f to the next planet in their solar system. The signal reflects back and is recorded as having a frequency f space apostrophe which is lower than the original signal.

      A few days later they repeat the experiment and find that the frequency change is less than that observed in the first experiment.

      Which of the following could cause these effect?

      1. The atmosphere of the planet is rotating such that the radio beam reflects off a section that is moving away from the alien's planet 
      2. The planet is moving away from the alien's planet
      3. The atmosphere of the planet is rotating such that the radio beam reflects off a section that is moving towards the alien's planet 
      4. The planet is moving towards the alien's planet

      • I only

      • I and II

      • I and II, followed by II and III

      • Various combinations of I, II, III and IV

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      2
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      In a binary star system, two stars orbiting each other can be observed using a spectrometer. The star system as a whole is moving away from the Earth at a constant velocity. The spectral lines appear to fluctuate. A graph can be plotted of relative velocity of each star compared to the observer.

      4RdJX-Vb_9-5-ib-hl-mcqs-hard-q6-question

      (a)
      At which point on the graph will the stars be in the following position?
      5irv5ae-9-5-ib-hl-mcqs-hard-q6-markscheme5irv5ae-9-5-ib-hl-mcqs-hard-q6-markscheme

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        3
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        Photographs of lines in the spectrum of the Sun show changes in wavelength. The atmosphere of the sun rotates at a speed u subscript s, anti-clockwise as observed from its north pole.

        What is an expression for the observed change in wavelength lambda apostrophe of a spectral line from light emitted from the right hand edge of the Sun as viewed from the northern hemisphere on the Earth?

        Assume the Earth's orbit is circular.

        • lambda apostrophe equals lambda open parentheses 1 minus u subscript s over c close parentheses

        • lambda apostrophe equals lambda open parentheses 1 plus u subscript s over c close parentheses

        • lambda apostrophe equals lambda open parentheses 1 minus c over u subscript s close parentheses

        • lambda apostrophe equals lambda open parentheses u subscript s over c minus 1 close parentheses

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        4
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        The graph shows the dominant wavelength of light emitted by 4 different stars, and the same light observed from the Earth.

        brvkbczv-9-5-ib-hl-mcqs-hard-q9-question

        Which pair of stars are moving away from Earth at the same speed?

        • 1 and 2

        • 2 and 4

        • 3 and 4

        • 1 and 3

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