Doppler Effect

Category:Pre-assessment

Learning Objectives:

1. Students will record an observation.
2. Students will draw a model to explain their observation.
3. Students will draw an example of the Doppler Effect with both sound and light.
4. Students will construct a concept map explaining their understanding of the Doppler Effect.
5. Students will relate the Doppler Effect to the movement of the stars.

Materials:

• Alarm clock or constant pitch noise maker that is capable of being swung around on a string.
• Wave Tank (optional)
• Slinky or spring
• Duct tape, string, padding
• Electromagnetic spectrum chart indicating the relationship between color and wavelength of visible light.
• Cafeteria trays - 1 per group
• Eyedroppers - 1 per group
• Clear flat-bottom dish and overhead projector

Sequence and duration of each part of lesson:

WATER WAVES

• Activity:
  • Divide class into groups of 3-4 students.
  • Give each group 1 tray and 1 eyedropper.
  • Put about 1/4 or 3/8 inch of water in each tray.
  • Have students use the eye dropper to drop water in the tray at regular intervals (eye dropper to remain stationary.)
  • Have students draw their observations.
  • Have students move the eye dropper (source of wave making) while dropping the water.
  • Have students draw their observations.
• Demonstration:
  • Place the flat-bottom dish on an overhead and produce waves by squeezing drops of water out of the dropper at regular intervals.
  • This should produce waves of the same wave length.
  • Continue to make waves while moving the source toward one end of the dish.
• These are examples of questions and discussion that this activity should draw out:
  • Define wave length, crest, trough, frequency.
  • Notice that the wave lengths are the same at both ends of the dish as the source of the waves stays stationary.
  • Notice that as the source moves, the waves are being produced at the same rate and travel at the same speed. Have students draw their observations on the worksheet. (Wave lengths should be shorter in the direction of the source and longer on the other end of the tank.)

SOUND WAVES

• Activity:
  • Have students stand around the outside of the room while the teacher swings the noise maker around on the string. Ask students to raise their hands when they notice a change in pitch (frequency).
  • Have students record their observations on the worksheet. (Students should note that the pitch of the noisemaker changes.) Have students share their observations and come to a consensus about what they heard.
• These are examples of questions and discussion that this activity should draw out:
  • Relate the water waves to sound waves.
  • The source of waves always produces waves at the same rate and the waves travel at the same speed.
  • Notice that the waves "bunch up" or "spread out" depending upon the direction the source is moving.
  • Moving the source results in higher or lower pich of the sound. Can you change the pitch without moving the source? (Yes.) How? (Move the observer.)

• Activity:
  • Use a slinky or spring to demonstrate waves being bunched up and spread apart (high frequency and low frequency)
• These are examples of questions and discussion that this activity should draw out:
  • Light travels in waves.
  • Colors of light are related to wave length.
    • (Show a chart of the spectrum of light that shows colors.)
  • Relate how pitch and color are determined by wavelength.
    • Relate doppler effect with red shift of stars a - what questions and discussion should draw out:
      • Each edge of the sun gives a shift: one red and one blue.
      • The side with a blue shift is moving towards us while the side with a red shift is moving away from us.
      • This is one way we know the sun rotates.
    • Ask students: how would we know if stars are moving away from us or towards us?
      • (answer- away- red shift low frequency; towards- blue shift high frequency)
    • Ask students: if several stars are moving away from us could we determine if one is moving faster away from us than another? Can we tell if we are moving away from the star or is it moving away from us?
      • (answer-the faster the stars are moving away the more the red shift.
    • *Discuss relative motion- the source can be moving or the observer can be moving or both the source and the observer can be moving.
  • Evaluation:
    • Evaluate the students drawings of both their observation and examples of the doppler effect and their worksheet.

• Tape recorder activity need two portable tape recorders and a car. Have one recorder in the auto recording. The outside observer also recording. As the car approaches the out side observer (100') start the horn and maintain it until about 100' pass the outside observer. When car and outside observer are across from each other have the observer yell to record his/her voice on both recorders. Should be able to play back recorders and hear a pitch change on one and not on the other.
• Spring and drill activity easy way to create a standing wave. Fix one end of a spring to a wall or table. Attach the other end to a bent i-bolt. Put the i-bolt into a varible speed drill. Start the drill and at diferent speeds, standing waves will be formed.

DOPPLER WORKSHEET

NAME___________________
PERIOD______
DATE _________

PART 1 - WATER WAVES

1. Draw a cross section of a water wave.
   
   
   
   
   
   
   
   
   
   
2. Define or show wavelength, crest and trough.
   
   
   
   
   
3. Draw observation of waves in tank when source is stationary.
   
   
   
   
   
   
   
   
   

1. When the teacher swung the noise maker around, what did you observe?
   
   
   
   
   
   
   
   
   
   
2. Describe the pattern of hand raising by the students.
   
   
   
   
   
   
   
   
   
   
3. How do you explain the above obsevation? Draw a picture to explain.
   
   
   
   
   
   
   
   
   
   
4. Give three examples of the doppler effect observed in the community.
   
   A.
   
   B.
   
   C.
   
   

1. Fill in blanks and answer "why" in each case. He sees _______ light she sees green light he sees _______light.
   
   

1. You see two stars in the distance and you wonder if they are rotating around each other like the ends on a baton. How could you use the doppler effect to check if they were or were not rotating around each other?
   
   
   
2. Complete the table by indicating the changes cause by the doppler effect.
   
   

   Source	Wavelength	Sound Waves	Light Waves
   Moving Towards You
   Moving Away from You

3. Construct a concept map using some or all of the following words: waves, sound, light, pitch, frequency, relative movement, stars, red shift, and any other word or words you think appropriate. Below is an example.