Lesson 10.3.1

10.3.1 Doppler effect and redshift Quiz: Pearson Edexcel Physics, Unit 10

20 questions

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Lesson 10.3.1, Doppler effect and redshift: 20 multiple choice questions for the Pearson Edexcel Physics (9PH0), Unit 10: Space, written with Revision Ninja.

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The 20 questions

  1. When a source of waves moves away from an observer, what happens to the observed wavelength?

    • It stays the same, since the source is moving.
    • It increases, which is a redshift.
    • It doubles, regardless of the speed.
    • It decreases, which is a blueshift.

  2. For a source receding at a speed much less than c, which expression gives the redshift z?

    • z = c v
    • z = v^2 / c
    • z = v / c
    • z = c / v

  3. What does the cosmological redshift of distant galaxies provide evidence for?

    • The constant luminosity of all stars.
    • The expansion of the universe.
    • The fixed age of the universe.
    • The presence of a central black hole in every galaxy.

  4. What does Hubble's law state?

    • The recession speed of a galaxy is proportional to its distance, v = H0 d.
    • The temperature of a galaxy is proportional to its redshift.
    • The luminosity of a galaxy is proportional to its distance.
    • The wavelength of light is inversely proportional to distance.

  5. A source moves towards an observer. What happens to the observed frequency?

    • It increases, which is a blueshift.
    • It decreases, which is a redshift.
    • It becomes zero.
    • It stays the same, since the source is approaching.

  6. A spectral line with rest wavelength 656 nm is observed at 660 nm. What is the approximate recession speed? Use c = 3.0 x 10^8 m s^-1.

    • 4.0 x 10^5 m s^-1
    • 6.6 x 10^6 m s^-1
    • 1.8 x 10^6 m s^-1
    • 1.8 x 10^8 m s^-1

  7. A galaxy has Hubble constant H0 = 70 km s^-1 Mpc^-1. What is its recession speed at 100 Mpc?

    • 70 km s^-1
    • 14000 km s^-1
    • 7000 km s^-1
    • 700 km s^-1

  8. A galaxy recedes at 2100 km s^-1 with H0 = 70 km s^-1 Mpc^-1. What is its distance?

    • 3 Mpc
    • 300 Mpc
    • 30 Mpc
    • 0.03 Mpc

  9. A line of frequency 5.0 x 10^14 Hz is observed at 4.9 x 10^14 Hz. What is the approximate recession speed? Use c = 3.0 x 10^8 m s^-1.

    • 1.5 x 10^8 m s^-1
    • 6.0 x 10^6 m s^-1
    • 2.0 x 10^7 m s^-1
    • 6.0 x 10^5 m s^-1

  10. A galaxy has redshift z = 0.2. What is its approximate recession speed? Use c = 3.0 x 10^8 m s^-1.

    • 6.0 x 10^8 m s^-1
    • 1.5 x 10^7 m s^-1
    • 3.0 x 10^8 m s^-1
    • 6.0 x 10^7 m s^-1

  11. Why is the Doppler formula v = z c used only for speeds much less than c?

    • Light cannot be shifted at any speed greater than zero, so the formula never applies.
    • Galaxies never move faster than the speed of sound in interstellar gas, so it holds.
    • At higher speeds relativistic corrections are needed, so the approximation fails.
    • The formula only works for radio waves and never for visible light or other spectra.

  12. A galaxy's spectral line is shifted by 1.0% from its rest wavelength. With H0 = 70 km s^-1 Mpc^-1, roughly how far away is it?

    • about 430 Mpc
    • about 0.43 Mpc
    • about 43 Mpc
    • about 4.3 Mpc

  13. Galaxy B is twice as far from Earth as galaxy A. Using Hubble's law, what is B's recession speed compared with A's?

    • Twice A's speed
    • Four times A's speed
    • The same as A's speed
    • Half A's speed

  14. A spectral line emitted at 486 nm is observed at 500 nm. What is the redshift z?

    • 0.029
    • 2.9
    • 0.34
    • 0.0097

  15. Why does the Doppler effect for light from a receding star show a shift to longer wavelengths?

    • The star's light is slowed down by its own gravity as it leaves the galaxy.
    • Light always becomes redder as it travels through space regardless of its motion.
    • The source recedes, so each crest is emitted farther away than the last.
    • The star emits light at a lower temperature when it moves away from the observer.

  16. Which statement about a Doppler shift for a source moving directly away from an observer is correct?

    • The observed frequency is unchanged.
    • The observed wavelength is shorter than the emitted wavelength.
    • The observed frequency is lower than the emitted frequency.
    • The observed frequency is higher than the emitted frequency.

  17. A galaxy's light shows a Doppler shift of z = 0.05. What is its approximate recession speed?

    • 5.0 x 10^5 m s^-1
    • 1.5 x 10^7 m s^-1
    • 1.5 x 10^6 m s^-1
    • 6.0 x 10^7 m s^-1

  18. A galaxy's spectral line with rest wavelength 500 nm is observed at 520 nm. What is its redshift?

    • 0.04
    • 0.02
    • 4.0
    • 0.96

  19. A star approaches Earth at 3.0 x 10^6 m s^-1. What is the approximate fractional change in observed frequency, Δ f / f?

    • 0.10
    • 0.0010
    • 1.0
    • 0.010

  20. Which observation shows that a galaxy is moving towards the Earth?

    • Its spectral lines are shifted to longer wavelengths, which is a redshift.
    • Its spectral lines do not change at all.
    • Its spectral lines are shifted to shorter wavelengths, which is a blueshift.
    • Its luminosity increases as it moves away.

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