# Stopping Voltage in Photoelectric Effect

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The stopping voltage is the voltage that one would apply to stop the electrons from migrating to the cathode. My quest is what purpose does this serve and what does the stopping voltage tell us?

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I don't know what sort of apparatus you are talking about, but I recently learned about the photoelectric effect.

Photoelectric Effect - many metals emit electrons when light (electromagnetic radiation) is shined on them. The photoelectric effect is an instance where electromagnetic radiation behaves like a particle (called "photon") rather than a wave.

Waves vary in both frequency and amplitude. However, the energy (E) carried by each individual photon of a wave is determined by the wave's frequency (υ), not its amplitude.

E = hυ

(h is planck's constant)

For the photoelectric effect to occur, each individual photon must have enough energy to dislodge an electron, thus the wave must have a high enough frequency. However, different metals have different threshold frequencies.

Edited by Mondays Assignment: Die
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Thanks for the insight. I am actually referring to the device used here

(

).

I understand the mechanics and theory of the photoelectric effect but never heard of Stopping Voltage. So I just wanted some clarification about its purpose and why it is important to calculate it.

Edited by blazinfury
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The stopping voltage where the current goes to zero is proportional to the KE of the electron.

$h\nu = E_I + KE$

Simply detecting a photocurrent doesn't tell you the electron's energy. You could try and find the photon energy where the PEE just barely works, but what if you don't have a continuously-tunable light source? (which most people don't). But a retarding potential is easily tuned.

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Awesome. Thanks for the great explanation

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