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Homework Help: Stopping potential and electron state?

  1. Mar 31, 2013 #1
    Hi guys, if an electron emitted by the photoelectric effect has E=hf-phi=KE of the electron=eV where V is the stopping potential, what will happen to the electron when a reverse potential (stopping potential) is being used? I'm guessing initially, the KE of the electron is of a positive value, the negative stopping potential now will cause it to be pushed backward back to the cathode where it is emitted, thus causing no electron to reach the anode. If this is true, then
    1. What will happen to the electron? Will it be in a superposition of escaping the surface and being grounded in the surface again, since KE=0 and the electron doesn't try to escape?

    2. Can I say the electric field caused by the stopping potential is exerting a negative force on the electron? If yes, is it doing negative work on the electron too, since the electron must be escaping initially at a speed but the speed is 0 ultimately?
  2. jcsd
  3. Mar 31, 2013 #2


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    As the electron feels a repelling force it will move back towards the photo cathode and it can strand on it.
    Yes, you are right. When you apply a stopping potential, you make the electrode opposite to the photocathode negative with respect to it. That means a repelling force for the photoelectron. The force does negative work on the electron, so decreases its kinetic energy, till it stops. After that, the electron accelerates backwards.
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