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    AAAAAAAAHHHHHHHHHHH, some1 help me. Whats a stopping potential? cant seem to define it easily and all the papers i have tried looking at have wierd questions. Can sum1 give me a definition and the context it will be found in, in a question.? Thanx
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    (Original post by scaredashell)
    AAAAAAAAHHHHHHHHHHH, some1 help me. Whats a stopping potential? cant seem to define it easily and all the papers i have tried looking at have wierd questions. Can sum1 give me a definition and the context it will be found in, in a question.? Thanx
    :confused:
    is the minimum reverse potential applied across the emitted electrons in order just to stop them all
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    basically...it's when you have a circuit with a cathode and an anode, where the cathode is made of a substance which emits electrons via the photoelectric effect. By illuminating the cathode with UV light of the right frequency, photoelectric emmision occurs and the fastest electrons also gain enough kinetic energy to go to the anode.

    However, the anode is made negative as well to repel the incoming electrons and is also connected to a potentiometer. First use a low voltage and all the electrons reach the anode. However when you increase the voltage across the anode, it becomes more positive and repels the high kinetic energy electrons. Soon, none of the electrons will reach the anode and you will get a zero reading on a picoammeter connected to the circuit.

    What does this mean?

    Well, the instance that the electrons with the highest KE (ie. ones at the surface of material) do not reach the anode, the voltage reading on the potentiometer is the force stopping the electrons.

    Therefore.... ½mv² lost = qV gained (electrical energy),

    (where V is the stopping potential, the voltage across the anode which prevents the highest KE electrons from reaching the anode)

    So stopping potential is proportional to the KE of the fastest electrons in a sample.

    Hope that helps


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