Doppler Effect

SAS Start this activity by clicking here. 

Login using the provided username (you won’t need a password). Read the directions on the first page. Follow the steps (Read, Research, and Respond). 

Use the this handout for your responses instead of the response sheet provided by the website.

 Submit your completed handout at the Doppler Effect Assignment. 

The Doppler Effect

What is the Doppler effect, and why is it important to understand?

Sound

1. Describe what is meant by “sound.” Explain how sound is created, transmitted, and sensed.

2. Set the source velocity (the Italian label reads Velocidad del emisor) to 0.0. Run the simulation (click the Empieza button). Calculate the frequency of the waves by counting the number of full waves that pass through a point in ONE second. You can press the Pausa and Continua buttons to step through the animation to pause and restart the wave motion.

3. The distance between numbered tick marks is 1 meter. Measure the wavelength using these tick marks. Use the wavelength and the frequency you calculated in number 2 to calculate the velocity of the wave.

The Doppler Effect in Sound

4. Now, set the source velocity (Velocidad del emisor) equal to 0.50. Run the simulation until the wave source (red rectangle) has moved close to the observer (blue rectangle). Calculate the new wavelength for the waves
on each side

of the moving source? Count the tick marks in one full wave to make this calculation, knowing that each tick mark equals 0.2 meters.

5. Examine the motion of the waves. Has the frequency increased or decreased on each side of the source?

6. Use the equation x f = v, to calculate the frequency at a point on each
side of the source. Remember that the velocity of the wave DOES NOT change (so use the velocity you calculated in #2). You will also use the wavelength you calculated for the wavelengths of the waves on each side of the source for #4.

7. Use the equations provided on page 2 of the Read section to calculate what the frequency actually should be on each side of the source (show your work below). Use this to see how accurate your answers in #6 were.

Electromagnetic Waves and Light

8. Summarize how electromagnetic waves are similar to acoustical (sound) waves. How are they different?

The Doppler Shift in Light

9. How is the Doppler shift used in astronomy? What is meant by the terms red-shift and blue-shift?

Summary (Homework)

10. Radar is a process that uses reflected electromagnetic waves in order to create an image of an object. Doppler radar (often used in weather) is used to tell the speed and direction clouds are moving. Explain how this might work. (Hint: Think about how radio waves might change when they reflect off of moving objects.)

11. 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.

12. Now answer the Focus Question. What is the Doppler effect, and why is it important to understand?