Doppler Simulation

Description:

This simulation shows waves being produced by a moving source. The crests of the each new wave shows up as an expanding circle around the source. Because the source is moving, the wavelenghts are spaced differently in front of the source than they are behind the source, causing an appearent wavelenght shift for observers to the left or right of the source.
  • Click the Run button to start.
  • You can adjust the speed of the source with the slider bar at the bottom.
  • The source location is given by 'Source x'. The center of the box is x = 0.
  • Clicking 'Classical' means the simulation uses the equation for the Doppler shift for sound.
  • Clicking 'Relativistic' means the simulation uses the equation for the Doppler shift for light.

Questions:

  1. How does an observer to the right of the source measure the wavelenght of the moving source, compared to its real value (the source moves towards the observer)?
  2. How does an observer on the right measure the frequency of the source, compared to its real value (the source moves towards the observer)?
  3. If the wave produced is a sound wave, does the observer on the right perceive the pitch as higher or lower?
  4. If the wave produced is a sound wave, does the observer on the left perceive the pitch as higher or lower?
  5. If the wave produced is a single frequency light wave (a single color), what change in color from the orginal will an observer on the left see?
  6. Wait until the source is about half way across the box and then move the speed slider all the way to the left so that the speed of the source is zero. What happens to the spacing of the waves in front and behind the source after waiting a minuit or so?
  7. If a car goes past with its radio on we easily hear the Doppler shift for sound. But if a car goes past with its lights on we do not notice the Doppler shift for light from the tail lights. Explain why this is so.
  8. Start a 'Classical' simulation with a slow source speed and then push the speed slider all the way over to the right (fastest speed). Describe what you see. What does this tell you about the speed of the source compared to the speed of the wave?
  9. Start a 'Relativistic' simulation with a slow source speed and then push the speed slider all the way over to the right (fastest speed). Describe what you see. What does this tell you about the speed of the source compared to the speed of the wave?
  10. Explain the reason for the difference between the Classical and Relativistic cases.