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About stopping potential

  1. Apr 21, 2015 #1
    For this post, I'll be mainly referring to this photoelectric equation:
    Fig 1: Photoelectric equation

    1) Is 'e' the charge of an electron, ie. a negative value? Or just an elementary charge, ie. a positive value?

    2) Is stopping potential (Vs) a positive or negative value? Because in my lecture notes, there's two different graphs, one saying that Vs is positive, and one saying that it's negative:

    Fig 2: Current against Potential difference graph

    Fig 3: Stopping potential vs Frequency graph

    2) Googling 'stopping potential vs frequency graph' yields me almost similar results of this graph:

    Fig 4: Stopping potential vs Frequency graph

    Must threshold frequency necessarily be the x intercept? Can it be any higher value, like the one shown in Fig 3?

    Last edited: Apr 21, 2015
  2. jcsd
  3. Apr 21, 2015 #2


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    Hmm... it looks like an elementary charge, but that does not fit to the sketch later. Let's say it is the charge of an electron.

    You can choose that in the experiment. The voltage where the current goes to zero is always "stopping" (the object where the light hits has a higher electric potential).

    Yes. That is the minimal frequency where you get electrons out of the material.
  4. Apr 24, 2015 #3
    As the terminals attached to the battery are changed for stopping the emission of electrons, after few minutes galvonometer stops deflecting and reaches to zero . Even though light rays are incident on photographic plate electron emission stops and thus stopping potential remains constant .
  5. Apr 24, 2015 #4
    For stopping potential, photographic plate should be attached with positive terminal so that electrons emitted does not move towards collector . Electric current and stopping potential becomes zero
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