IBPhysicsHLExam QuestionsWave BehaviourDoppler Effect

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First teaching 2023

First exams 2025

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Doppler Effect (HL 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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    A team of naturalists are researching the movement of whales in the ocean. They plan to calculate the velocity of a whale using the Doppler effect. The whale pod is moving towards the research team who are in a stationary boat.

    Which equation will allow the researchers to investigate the velocity of the whales using the frequency of sound in water?

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

    • f space apostrophe space equals f space open parentheses fraction numerator v over denominator v plus u subscript s end fraction close parentheses

    • f space apostrophe space equals f space open parentheses fraction numerator v plus u subscript 0 over denominator v end fraction close parentheses

    • f space apostrophe space equals f space open parentheses fraction numerator v over denominator v minus u subscript s end fraction close parentheses

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    3
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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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    4
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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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    5
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    Which equation can be used to calculate the Doppler shift for the sound of a person running away from an observer whilst blowing a whistle?

    • f space apostrophe equals f space open parentheses fraction numerator v plus u subscript 0 over denominator v end fraction close parentheses

    • f space apostrophe equals f space open parentheses fraction numerator v over denominator v minus u subscript s end fraction close parentheses

    • f space apostrophe equals f space open parentheses fraction numerator v minus u subscript 0 over denominator v end fraction close parentheses

    • f space apostrophe equals f space open parentheses fraction numerator v over denominator v plus u subscript s end fraction close parentheses

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    6
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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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    7
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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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    8
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    Which of the following equations will give an increase in the frequency of the observed wave according to the Doppler Effect?

    • f space apostrophe equals f space open parentheses fraction numerator v minus u subscript o over denominator v end fraction close parentheses

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

    • f space apostrophe equals f space open parentheses fraction numerator v plus u subscript o over denominator v end fraction close parentheses

    • f space apostrophe equals f space open parentheses fraction numerator v over denominator v plus u subscript s end fraction close parentheses

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    9
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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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    10
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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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    A train is moving away from an observer on a platform with a constant speed v over 17 where v is the speed of sound. The train emits sound of frequency f.

    What is the observed speed of sound and the observed frequency as the train recedes?

     

    Observed speed of sound

    Observed frequency

    A.

    		 v fraction numerator 18 f over denominator 17 end fraction

    B.

    		 v over 17 fraction numerator 18 f over denominator 17 end fraction

    C.

    		 v fraction numerator 17 f over denominator 18 end fraction

    D.

    		 17 v fraction numerator 17 f over denominator 18 end fraction

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      2
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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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      3
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      A car travels in a straight line towards a stationary observer at a speed of 0.2v, where v is the speed of sound. The car's horn emits a pure sound of frequency ƒ.

      What is the frequency of the sound of the horn as heard by the observer?

      • 0.80f

      • 1.25f

      • 0.83f

      • 1.20f

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      4
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      An observer approaches a stationary source of sound. The speed of the emitted sound and its wavelength, measured at the source, are nu and λ respectively.

      Which of the following is the observed wave speed and the observed wavelength, as measured by the moving observer?

       

      Observed wave speed

      Observed wavelength

      A.

      		 > v <  λ

      B.

      		 = v >  λ

      C.

      		 < v >  λ

      D.

      		 = v <  λ

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        5
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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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        6
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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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          7
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          A siren on a fire engine emits sound of wavelength λ. The speed of sound in still air is v.

          What would be the wavelength of the sound recorded by a stationary observer when the ambulance travels towards them at speed of 0.15 v?

          • 0.85λ

          • 1.15λ

          • 0.15λ

          • 7.67λ

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          8
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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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          9
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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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          10
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          A car of terrified observers drive away from a stationary, but hungry T. rex, at a speed of 10 m s−1. They hear the roar of the T. rex at a frequency of 170 Hz. The speed of sound in air is 340 m s−1.

          What is the frequency of the sound as emitted by the T. rex?

          • 175 Hz

          • 165 Hz

          • 120 Hz

          • 220 Hz

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          1
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          A stationary source emits sound wave with frequency f. An observer moving towards the source measures the sound as having frequency f space apostrophe. The speed of the observer is 20% of the speed of sound.

          What is the the value of f space apostrophewhen the emitted frequency is 10 Hz?

          • 0.8 Hz

          • 1.2 Hz

          • 10.2 Hz

          • 12 Hz

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          2
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          The flow of blood can be monitored using a machine which emits ultrasound of 10 MHz and is then able to measure the change in frequency when the pulse returns having reflected off a red blood cell.

          When a wave is reflected from a moving object, the change in frequency is doubled compared to a situation where a sound is detected by a moving observer. Assume that the speed of sound in the body is the same as that of water, 1500 m s–1.

          What is the frequency detected if blood is flowing away at 0.15 m s−1?

          • 10.002 MHz

          • 2000 Hz

          • 9.998 MHz

          • −2000 Hz

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          3
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          A boat sits on a lake, and is hit by 4 waves every 10 s. As the boat starts to move in the same direction as the waves, exactly 2 waves from behind hit the boat every 10 s. The speed of the boat is 1.5 m s−1.

          What is the speed of the waves?

          • 1.5 m s−1

          • 3 m s−1

          • 1500 m s−1

          • 340 m s−1

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          4
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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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            5
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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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            6
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            An asteroid which entered the Earth's atmosphere 64 million years ago emitted a sound of frequency 100 Hz due to the interaction with the atmosphere on its entry.

            A T. rex directly under the asteroid hears the noise, but hears it at a frequency of 200Hz. The distance from the top of the atmosphere to the ground is 102 km. 

            28yjpt61-9-5-ib-hl-mcqs-hard-q8-question

            How long does the T. rex have before the asteroid hits?

            • 10 minutes

            • 170 s

            • 170 mins

            • 6000 s

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            7
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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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            8
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            A bat is flying towards a tree using echolocation to navigate. The bat emits an ultrasound pulse of 45 kHz. On reflection from the tree, the bat detects a frequency of 50 kHz. The bat is 170 m away from the tree. Due to reflection, the speed of the bat is halved because the Doppler effect is doubled.

            How long does the bat have to change course before hitting the tree?

            • 170 s

            • 10 s

            • 5 s

            • 1 s

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