Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

What are the amplitudes called for blue visible light, and microwaves?

  1. May 11, 2008 #1
    The amplitude of sound waves is commonly referred to as volume. What about for blue visible light, and microwaves? I'm guessing for the first one it's brightness. Btw I'm looking for a word answer, not the magnitude of the amplitude (not a numerical amplitude)

    Thanks for reading.
  2. jcsd
  3. May 11, 2008 #2


    User Avatar
    Science Advisor

    Intensity. Amplitude. The question sounds more like a dictionary rather than a physics question.
  4. May 11, 2008 #3


    User Avatar

    Staff: Mentor

    Btw, blue light and microwaves are different frequencies, not amplitudes. But mathman is right - the terminology is the same.
  5. May 11, 2008 #4
    Minority viewpoint: there is an interesting question behind this. Professional sound folks measure SPL ... sound pressure level ... to assess the amplitude or volume of sound. RF people measure 'Volts Per Meter' from a Field Strength meter as a measure of the E field of a source, and call it field strenth or intensity. By the time you get to light we don't measure the peak of the electric field, we measure the intensity, the average energy delivered, and we do that with detectors that have a 'quantum efficiency'.

    So on the one hand, they are all the same thing: amplitude is amplitude. On the other hand, the huge change (sound at kilohertz to light at 100's of terrahertz) in scale allows us to use comfortable classical concepts for sound and radio waves, while light is better handed with photon and quantum efficiencies.

    If you think this doesn't matter, consider the difference in output from a sound transducer, which outputs a waveform proportional to the pressure field, and the output from a photodiode, which outputs a current proportional to the incident light energy (# electrons proportioanl to # photons).
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook