The Physics
Opus in profectus


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  1. A 32.83 ms fragment of the EBS alert tone is shown in the oscilloscope display below. (The full tone lasts 22.5 seconds.) The beat structure is plainly visible at this scale. There are approximately 3.5 cycles of the beat and 29.75 cycles of the carrier visible in the display window. Determine the frequencies of the two tones used to produce the alert.

    Screenshot of an oscilloscope application window

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


  1. The telephone "off the hook" warning in the United States is composed of four pure tones: 1400, 2060, 2450, and 2600 Hz.
    1. How many beat frequencies are present in this combination?
    2. What are the beat frequencies?
  2. A student has two tuning forks, one with a frequency of 349 Hz and the other with an unknown frequency. When struck together, the tuning forks produce three beats per second. What are all the possible frequencies of the unknown tuning fork?
  3. As a part of a performance, a vocal trio sang the following three notes: C 264 Hz, F 352 Hz, and A 440 Hz. After the performance your friend who was at the performance with you makes the following observation: "When the trio sang those three notes it sounded like there were more than three singers. Hey, you took physics! How did they do that?"
    1. Explain in no more than three sentences how it is possible for three people to produce more than three notes while singing.
    2. What are the frequencies of the extra notes?