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I Does photoelectric effect include light with threshold freq?

  1. Apr 25, 2016 #1
    I know the definition of photoelectric effect : the release of electrons from a metal when it is in contact with electromagnetic waves..
    However, my question is.. If a light wave hits a metal and that photon has freq = threshold frequency of that metal, does this mean that the energy of the photon is just enough to release the electron from the surface of the metal but the electron does not have kinetic energy to further continue motion and hence there is no photocurrent??

    If so, then is the above scenario also considered to be photoelectric effect or does photoelectric effect only refer to when light has frequency above the threshold frequency and hits metal to cause electrons to actually move??

    Please answer the above 2 qns!! Thanks!! :-)
  2. jcsd
  3. Apr 25, 2016 #2


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    Hello Polly, :welcome:
    Yes, that's rather what PF is there for :smile: . No reason to expect something other than that, is there ?

    Threshold frequency is indeed the term used for the situation you describe. It's something to compare different materials. The real situation is statistical and on an atomic scale. In reality you don't get the sharp pictures like in the books
    Hehe, yes: a photoelectric effect without an effect that's somewhat observable. Physics is generally an exact science (up to a point :smile:), but we communicate with (imperfect and less exact) language and -- like taste -- that's always debatable.
    Alternative answer: the existence itself of the thus described cutoff frequency is the photoelectric effect. It has great historical weight.

    Happy PFing !
  4. Apr 25, 2016 #3
    hmm that makes sense, thanks for that!

    However, what offers a contradicting idea about photoelectric effect is the link below..


    it states that photoelectric effect is defined as 'when light ABOVE the threshold frequency hits a metal.. electrons are escaped'..

    it does not state that the effect includes when light HAS the threshold frequency..

    Any idea what it actually means?
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