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The main idea of the photoelectric effect

The basic idea of the photoelectric experiment is as follows.

By shining light on a metal target we see that electrons are ejected. These electrons create a detectable current. By applying a voltage to the circuit, we can change the current, and determine both the number of electrons ejected and their individual energy. By shining light with different frequency and various intensities, we can study in detail the interaction between light and electrons.

This seemingly simple experiment led to one of the most profound discoveries in physics. We will spend this whole week looking at this in more detail.

You can download the photoelectric effect simulation in the resources below, this is the simulation for your lab this week. Fig "Photoelectric setup" shows the basic setup and in the video, Dr. Leblond goes through the basic ideas.

Important Characteristics of the Photoelectric Effect

By doing the experiment and trying out things we found that

1. The measured current is directly proportional to the light intensity. If the light intensity is doubled, the current doubles.
2. The current appears without delays.
3. There is a threshold (minimum) frequency of light below which there is no current, no matter how intense.
4. This threshold frequency of light depends on the metal used as target.
5. By applying a reverse voltage, we can stop the current. The voltage necessary to do that is referred to as Stopping Potential V_{stop} .
6. The value of V_{stop} does not change as we change the intensity. But it does change if we change the frequency.

External Resources

• Run the simulation from the Phet website  using CheerpJ