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

Size of detectable objects

  1. Feb 6, 2014 #1
    Hi!
    In a book, there is stated that the least detectable object by a bat is when the object is λ/2 of the sound wavelength emitted by the bat. I know there is resolution criteria for light microscopes too, which concerns the wavelength of the light.

    My question is: Are these criteria about the phenomena of interference of waves or something else? Or maybe it is possible to detect the objects smaller than this size, but we can not get any information about size or form from them if the wavelength is too long?
     
  2. jcsd
  3. Feb 6, 2014 #2

    Drakkith

    User Avatar

    Staff: Mentor

  4. Feb 7, 2014 #3

    Andy Resnick

    User Avatar
    Science Advisor
    Education Advisor
    2016 Award

    There's at least one important difference between 'detecting' and 'resolving'- while 'resolving' does involve the wavelength of light (or sound), 'detecting' does not- detection only depends on the signal-to-noise ratio, which can be quite high even for subresolution objects. Also, it is true that detection of a subresolution object does not provide any information about the size/shape/etc. of the object.
     
  5. Feb 7, 2014 #4
    One good example is stars. Naked eye resolution is about 1 arc minute (60 arc minutes = 1 degree) so we can only resolve one star (the sun at ~30 arc minutes) but there are thousands of stars we can detect given reasonably dark skies (good SNR).
     
  6. Feb 9, 2014 #5
    Thanks for answers, everyone. Now I have a starting point for curious students asking about this task.
     
  7. Feb 9, 2014 #6

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    Bats have a significant amount of brain power and they can deduce a lot about what their target is without needing a high resolution sonar image. They can detect a target and know its distance. The strength of the return signal is a good indication of size because the reflectivity of their prey species will be much of a muchness (unlike the range of brightnesses of stars, for instance). They can then go closer and 'investigate' - unlike astronomers with their stars.

    Diffraction (resolution) limits, optical and sonar are a bigger problem when it comes to deciding whether it's one or two objects you are looking at. The eye can see many points of light up in the night sky which are, in fact two or more bright objects.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Size of detectable objects
  1. Time and Size (Replies: 17)

  2. Detecting Cations (Replies: 1)

Loading...