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Doppler Effect (Grade 9)

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Doppler Effect

Instructions: Read each question carefully. Choose the answer that best fits the question. Short answer response questions must be responded to in complete sentences. If the question involves calculations, you must show all your math work.

Due to the Doppler effect, when moving AWAY from the source of a sound,
  1. the pitch of the sound should get lower.
  2. the pitch of the sound should get higher.
  3. the sound should get louder.
  4. the sound should get more quiet.
The                      effect describes how the frequency of waves can appear to change if a source and observer are in motion relative to each other.
When a car is coming toward you, the pitch you hear is                   than when the car is moving away from you according to the Doppler Effect.
The Doppler Effect causes a change in perception of the pitch of source of sound because in the same period of time
  1. if the distance between source and observer increases, the waves must spread out.
  2. if the distance between source and observer decreases, the waves must be compressed.
  3. the same number of waves must fit between the source and the observer.
  4. All of the above are correct.
A car horn has a frequency of 400 Hz. The car is moving away from an intersection at 20 m/s. The frequency heard by a woman standing at the intersection could be
  1. 390 Hz.
  2. 400 Hz.
  3. 410 Hz.
  4. 420 Hz.
When an ambulance drives by your house with sirens blaring, the sound waves of the sirens are                        as it approaches and                        as it speeds away.
  1. lower; higher
  2. spread out; compressed
  3. higher; lower
  4. compressed; spread out
When a sound source approaches an observer, the
  1. pitch become lower.
  2. pitch becomes higher.
  3. light becomes bluer.
  4. light becomes redder.
When an object is coming toward you, the pitch you hear is lower than when it is moving away from you.
  1. True
  2. False
Explain the Doppler Effect. Include a real-world example in your explanation.

While standing in the 42nd Street and Times Square subway station, Rodney hears the incoming screech, registering at 4000Hz, of an express train speeding through the station at 18 m/s. What is the frequency of the approaching train that is perceived by Rodney’s ears?[math]f=f_0((v_"sound"+v_o)/(v_"sound"-v_s))=[/math]

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