# Photoelectric Effect: Measuring Stopping Voltage

• tomz
In summary, the photoelectric effect involves measuring the stopping voltage of photo-electrons by connecting a battery to the circuit and adjusting it until the current reaches 0. This is because waiting for all the photo-electrons to generate the voltage themselves is impractical and the system may discharge itself due to imperfect isolation. Additionally, not all electrons released have the maximum theoretical energy, resulting in a biased potential when using a voltmeter. The distribution in velocities also means that low velocity electrons do not play a part in the process once the voltage reaches their particular stopping voltage. Therefore, it is more practical to find the value of V that will stop the current, which is why it is recommended to use this method.

#### tomz

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!

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.

## 1. What is the photoelectric effect?

The photoelectric effect is a phenomenon in which electrons are emitted from a material when it is exposed to electromagnetic radiation, such as light.

## 2. How does the photoelectric effect work?

When a photon of light strikes the surface of a material, it transfers its energy to an electron in the material. If the photon has enough energy, it can break the electron free from the material's surface, resulting in the emission of an electron.

## 3. What is stopping voltage?

Stopping voltage is the minimum voltage required to stop the emission of electrons in the photoelectric effect. It is the voltage at which the kinetic energy of the emitted electrons is equal to the energy of the photons of light.

## 4. How do you measure stopping voltage in the photoelectric effect?

To measure stopping voltage, a circuit is set up with a light source, a photocell, and a variable voltage source. The voltage is gradually increased until the emitted electrons are no longer able to reach the positive electrode. The voltage at this point is the stopping voltage.

## 5. What is the significance of measuring stopping voltage in the photoelectric effect?

Measuring stopping voltage allows us to determine the energy of the photons of light that are causing the emission of electrons. This helps us understand the properties of light and the behavior of electrons in different materials.