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Integrated Coordinated Science for the 21st Century

Active Physics
+ Chapter 6
Is Anyone Out There?
Answers
Physics To Go
  1. a) The shape of the grooves matches the vibrations of the sound.
    b) On a CD, the sound is stored as numbers that give the sound loudness. There are about 40,000 of these numbers for every second of sound.
  2. a) An analog recording makes a representation (a groove in a record or a magnetic pattern on a tape) that changes just like the sound changes. The recording is literally an analog of the sound.
    b) A digital recording reduces the sound to a series of numbers.
    c) The grooves are shaped just like the sound vibrations.
    d) Information on the CD is stored in pits, which record the ones and zeroes in the numbers that represent the sound.
  3. a) A clock with hands is analog. The position of the hands changes smoothly at time progresses.
    b) A clock with numbers is digital. Each time is represented by a different number, rather than by a smooth change in the position of the hands.
  4. a) 150 s
    b) 40 X 103 X 150 = 6.0 X 106
    c) 8 X 6.0 X 106 = 4.8 X 107
  5. a) Analog.
    b) Sample it and find numbers to represent the loudness of each sample.
  6. a) 2.5 X 10-5 s
    b) About 20 Hz to 20,000 Hz
    c) 15,000 Hz
    d) 6.7 X 10-5
    e) At this frequency, two or three samples would be taken per period. That should be often enough to represent sound at that frequency.
  7. Each sampled sound is so short, and another follows it immediately.
  8. a) CDs store more music, they are not damaged by a needle during playing, they are more compact, minor scratches are not a problem, there is no noise during quiet periods of the music, their range of loudness and softness (dynamic range) is much greater, and their frequency response is more accurate.
    b) Some listeners believe that CDs distort the frequency response.
  9. Substantial damage to the surface would damage the sound. With careful handling, hardly anything can go wrong with a CD.
  10. More music will be stored on the same-sized disc. Perhaps a CD will be developed that will make a recording in the home, as in a tape recorder.
  11. a) The CD stores about 70 minutes of music. Each second contains about 40,000 samples. Each sample contains 8 digits (ones or zeroes). The total number of digits is:70 X 60 X 40,000 X 8 = 1.3 X 109
    b) The spectral lines of hydrogen, the location of the Sun in our galaxy, a Mozart piano concerto, a Beatles song . . .etc.
    c) Perhaps with drawings.