practice

  1. Write something.
  2. Write something else.
  3. Write something different.
  4. Write something completely different.

conceptual

  1. What effect does frequency have on the speed of sound in air? Describe a situation from everyday experience that could be used to verify your claim.
  2. A scene in a science fiction movie shows a spacecraft exploding in outer space. At the very same instant, the occupants of a second spaceship located a considerable distance away are shown reacting to the sound and light of the explosion. What two physics errors did the producers make in this scene?
  3. At some track events (the 100 m and 200 m dash, in particular) the start and finish lines are far enough apart that a person timing the event with a stopwatch will encounter a serious problem if they start timing when they hear the bang of the starter's pistol.
    1. Why shouldn't manually timed track events start at the sound of the starter's pistol?
    2. When should timing begin?

numerical

  1. What range of wavelengths in air at room temperature are audible to a human with ideal hearing?
  2. How long would it take a sound wave to travel completely around the earth? (The average surface temperature on earth is about 13.5 °C)
  3. How many seconds elapse between when a flash of lightning is seen and when the thunder is heard if the lightning is …
    1. 1 kilometer away?
    2. 1 mile away (1.6 kilometers away)?
  4. A measurement, a calculation, and a set of related questions.
    1. Measure the horizontal distance between your ears. (This is not easy to do. You will probably be off by a couple of centimeters, but that is OK. An approximate value is sufficient.)
    2. Approximately how long does it take a sound wave coming from a source on one side of your head to travel the distance between your ears? (This is known by audiologists as the interaural time difference or ITD.)
    3. What would happen to the value calculated in part b. if the source of sound was moved forward a bit (not closer to your ear, but in the direction you call forward — anterior, as they say in the medical professions)?
    4. What would happen to the value calculated in part b. if the source of sound was directly in front of you instead of off to one side?
    5. Your brain can actually perceive the interaural time difference (as long as you have two working ears). What does your brain use this information for?
  5. The moving part of an ultrasonic ranger is a gold-coated plastic disk that acts as both a loudspeaker and a microphone. The usual term for such a device is a transducer. (Transduction is the process of changing energy from one form to another, so this is a very generic name.) A typical ultrasonic ranger found in science classrooms emits a 1 MHz sound wave that is pulsed 50 times each second. The 1 MHz ultrasound is inaudible, but the human ear can hear the transducer click at the begriming of each pulse. At 50 clicks a second it emits a sound that is best described as a "buzz". During each pulse, the transducer is turned on for such a brief period that it is only able to vibrate 16 times. It then "rests" for 2.38 ms and "listens" for the echoes returning from whatever is in front of it. The circuitry attached to the transducer calculates the distance from the ranger to the object based on the return time of the echo and the speed of sound in air at room temperature (which is assumed to be 343 m/s at 20 °C).
    1. Calculate the wavelength of the sound emitted.
    2. Use the results of part a. to determine this ranger's resolution (that is, the smallest change in distance that can be detected).
    3. Calculate the length of the wavetrain emitted by the transducer.
    4. Calculate the distance the wavetrain travels during the "rest" period.
    5. Use the results of part d. to determine the smallest distance the ranger can measure.
    6. Calculate the time between the end of the "rest" period and when the transducer sends out its next pulse.
    7. Use the results of part f. to determine the largest distance the ranger can measure.
    Source: MacIsaac, Dan and Ari Hämäläinen. "Physics and technical characteristics of ultrasonic sonar systems." The Physics Teacher. Vol. 40, No. 1 (January 2002): 39-46.