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The Doppler Effect quiz #1

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  • Which type of motion of a star can be measured using the Doppler effect?
    The Doppler effect can be used to measure the radial motion of a star, which is its motion toward or away from the observer.
  • What is the Doppler effect?
    The Doppler effect is the change in frequency of a wave as measured by an observer due to the relative motion between the source of the wave and the observer.
  • Can the Doppler effect be observed with longitudinal waves, transverse waves, or both?
    The Doppler effect can be observed with both longitudinal and transverse waves.
  • Why does the frequency of a siren get higher as an ambulance using that siren gets closer?
    As the ambulance approaches, the sound waves are compressed, causing the observer to detect a higher frequency (higher pitch) due to the Doppler effect.
  • Why does a siren have a higher pitch as it approaches you?
    A siren has a higher pitch as it approaches because the sound waves are compressed, increasing the frequency detected by the observer.
  • How is the change in pitch perceived if a car passes a pedestrian?
    As the car approaches, the pedestrian hears a higher pitch; as the car moves away, the pitch drops to a lower frequency.
  • What is the Doppler effect used by weather forecasters to measure?
    Weather forecasters use the Doppler effect to measure the motion of weather systems, such as the speed and direction of moving air or precipitation.
  • Which scenario describes the occurrence of the Doppler effect?
    The Doppler effect occurs when there is relative motion between a wave source and an observer, such as a moving siren or a star moving toward or away from Earth.
  • What happens when a blaring siren moves away from you?
    When a siren moves away, the sound waves are stretched, resulting in a lower frequency (lower pitch) detected by the observer.
  • How can astronomers detect the Doppler shift of a star?
    Astronomers detect the Doppler shift of a star by measuring changes in the frequency or wavelength of the star's emitted light.
  • What is a good model for the Doppler effect?
    A good model for the Doppler effect is a moving sound source, such as a siren on a vehicle, where the pitch changes as the vehicle approaches and then recedes from an observer.
  • Why do people see distant events before they hear them?
    People see distant events before they hear them because the speed of light is much greater than the speed of sound.
  • How does the wavelength of electromagnetic radiation change during a Doppler shift?
    During a Doppler shift, the wavelength of electromagnetic radiation decreases (blue shift) if the source moves toward the observer and increases (red shift) if the source moves away.
  • Why does the Doppler effect detect only radial velocity?
    The Doppler effect detects only radial velocity because it measures changes in frequency due to motion directly toward or away from the observer, not perpendicular motion.
  • Does the Doppler shift occur for only some types of waves or for all types of waves?
    The Doppler shift occurs for all types of waves, including sound waves and electromagnetic waves.
  • What is an example of the Doppler shift?
    An example of the Doppler shift is the change in pitch of a train's horn as it approaches and then passes an observer.
  • If a yellow star is moving away from us very rapidly, what happens to its observed light?
    If a yellow star is moving away from us rapidly, its light is redshifted, meaning the observed wavelength increases and the color shifts toward the red end of the spectrum.
  • What does it mean if the spectra of most galaxies show redshifts?
    If the spectra of most galaxies show redshifts, it means their spectral lines are shifted to longer wavelengths, indicating the galaxies are moving away from us.
  • As you run toward a source of sound, how do you perceive the frequency of that sound?
    As you run toward a source of sound, you perceive the frequency to increase (the pitch becomes higher).
  • How does the pitch of a train's horn change as it passes by an observer?
    The pitch of a train's horn is higher as it approaches the observer and drops to a lower pitch as it moves away, due to the Doppler effect.