- Describe what is meant by “sound.” Explain how sound is created, transmitted, and sensed.
Doppler Effect Interface:
In the interface shown above the sound source (red box) is motionless. There are also two motionless observers (blue boxes). Assume the measurements in the interface are in meters. The tick marks between numbers are 0.2 meters each. It is common for sound waves to be shown with circles representing the wave front (the front of the compression part of the wave). Time is shown in the upper left hand corner next to the word tiempo.
- Use the video above (or here) to calculate the frequency (how many waves pass a given point per 1 second) for this situation. Don’t forget your units!
- Use the tick marks to measure the wavelength of the waves present. Remember that wavelength is the length of one full wave, so in this interface it is the distance between each wave front. Don’t forget your units!
- Use your frequency and your wavelength from the above questions to calculate the velocity of your wave using the equation v = λ x f. Don’t forget your units!
The Doppler Effect in Sound
Now watch the video below (or here) of the interface again, but now the source (red box) is moving with a velocity of 0.50 m/s.
- Examine the motion of the waves. Describe how the frequency changed on each side of the source.
- What is the new wavelength on EACH side of the moving source? (You should have twoanswers here.) Don’t forget your units.
- Remembering that the velocity of the wave HAS NOT changed (this means use the velocity you calculated above), use the equation v = λ x f and the wavelengths you measured above to calculate the new frequencies on EACH side of the moving source. Don’t forget your units.
Electromagnetic Waves and Light
- Describe several ways that electromagnetic waves are similar to acoustical (sound) waves.
- Describe several ways that electromagnetic waves and acoustical waves are different.
The Doppler Shift in Light
- How is the Doppler shift used in astronomy?
- What is meant by the terms red-shift and blue-shift?
- Radar is the process of sending out an electromagnetic wave, having it reflect off of a body (such as an airplane or a water molecule), receiving the reflected wave, and then imaging the results. How do you think the Doppler shift can be used to measure wind speeds (Doppler radar)? (Hint: Think about how radio waves might reflect off of air particles that are moving at various speeds and in various directions.)
- Explain why the pitch of an object approaching an observer (such as a fire truck with its siren on) differs from the pitch as it moves away from the observer. Remember that pitch is the brain’s interpretation of a sound’s frequency.
- What is the Doppler effect, and why is it important to understand?