Photoelectric Effect: Measuring Stopping Voltage

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Measuring stopping voltage in the photoelectric effect involves connecting a battery to the circuit and adjusting until the current reaches zero, rather than using a voltmeter. This is because relying solely on a voltmeter would be impractical, as it would require a large number of photo-electrons to generate a measurable voltage and would be affected by system discharge. Additionally, not all released electrons have the maximum energy, leading to a biased potential reading from a voltmeter. The distribution of electron velocities means that only electrons with sufficient energy contribute to the current once a certain voltage is reached. Therefore, determining the stopping voltage by measuring the current is a more effective and practical approach.
tomz
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Hi everyone, a quick question on photoelectric effect.

Why measure stopping voltage by connecting a battery to the circuit and then adjust until current reach 0? Cant we just use a voltmeter?


Thank you!
 
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In theory, you could wait until all the photo-electrons generate the voltage themself - but that would require so many photo-electrons that it is not practical. In addition, no isolation is perfect (especially with an attached voltmeter), the system would discharge itself.
 
mfb said:
In theory, you could wait until all the photo-electrons generate the voltage themself - but that would require so many photo-electrons that it is not practical. In addition, no isolation is perfect (especially with an attached voltmeter), the system would discharge itself.

Thanks. After some thinking I guess there is also the problem that not all electrons released have the theoretical maximum energy, so the potential get from a voltmeter will be biased
 
tomz said:
Thanks. After some thinking I guess there is also the problem that not all electrons released have the theoretical maximum energy, so the potential get from a voltmeter will be biased

The distribution in velocities will just mean that it takes longer to reach the maximum voltage - the low velocity electrons will play no part in the process once the voltage is greater than their particular stopping voltage.
Finding the value of V that will stop the current would be a more practical way, I think - which is why it's recommended.
 

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