Photocurrent

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BrianMBy
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Joined: Wed Jul 03, 2019 2:36 pm

Photocurrent

Post by BrianMBy »

Why does photocurrent plateau with voltage in photoelectric effect? As voltage increases, the electric potential energy of the ejected electron will increase. Thus by the time it reaches the anode its velocity will be dependent on voltage. Ie more will reach the anode per unit of time as voltage increases.
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joe
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Joined: Fri Aug 29, 2003 11:57 am
Location: Sydney

Re: Photocurrent

Post by joe »

Why does photocurrent plateau with voltage in photoelectric effect?
Good question.
As voltage increases, the electric potential energy of the ejected electron will increase. Thus by the time it reaches the anode its velocity will be dependent on voltage.
Correct.
Ie more will reach the anode per unit of time as voltage increases
That doesn't follow. Once the voltage is large enough, every electron that is liberated from the metal by a photon contributes to the current: none 'fall' back into the emitting surface. At higher voltages, that same number of electrons take less time to get there, but that doesn't change the number per second liberated from the surface, which equals the number per second arriving at the other electrode. With sufficiently high voltage, the current is limited by the number of (sufficiently energetic) photons and becomes independent of the voltage.
BrianMBy
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Joined: Wed Jul 03, 2019 2:36 pm

Re: Photocurrent

Post by BrianMBy »

Thanks for that Joe. It makes more sense now
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