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I Beats Production

  1. Mar 13, 2016 #1
    I was reading about superposition of two simple harmonic motions and beats. There were no examples given in my book. I was thinking if change of amplitude from a maximum to a minimum in periodic manner is referred to as beats, then we can realize it by either sound wave or light wave. Now my question is,
    1. Is light or sound wave simple harmonic ? I don't think so.
    2. Is there any other way to experience beats ?
     
  2. jcsd
  3. Mar 13, 2016 #2

    sophiecentaur

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    Mixing (beating) is a very common phenomenon. It's mainly a matter of spotting the effect occurring. It doesn't only happen with simple harmonic waveforms.
    1. A sinusoidal (sound) tone is, by definition, simple harmonic but you don't hear many of those except when they're produced electronically. A monochromatic light wave is also SH.
    2. You can get beats in pieces of machinery when there are two parts that are vibrating at different frequencies. You can sometimes get beat effects in your eyes when watching a tv picture if you hum loudly. ( using your peripheral vision it may be stronger). Moiree fringes (Google it) are also beats between two different spatial frequencies of grid pattern. PAL and NTSC colour TV used to suffer from terrible spatial beats due to intermodulation between high frequency patterns in the picture and the colour subcarrier. Announcers' shirts and suits had to be chosen without busy patterns, to avoid distracting the viewers.
    Radio receivers use mixing, to change signal frequencies (superheterodyne receivers) which shifts the wanted signal to an IF (intermediate frequency) for selective filtering etc.
     
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