Some students think a voltage source will help release photoelectrons
For example, they may think that if the energy supplied by the voltage source overtakes the work function of the metal, then photoelectrons can be released, even if the photon energy is less than the work function.
You might consider asking students to draw a current-voltage graph for an electrode with a work function that is larger than the photon energy. Students would be expected to draw a zero current graph. However, if students hold this incorrect idea, they are likely to draw a graph for a typical photoelectric experiment, where the work function is less than the photon energy. They may also draw a graph with a positive stopping voltage instead of a zero current graph.
Resources to Address This
Use this lesson outline to help plan and carry out a practical demonstration of the photoelectric effect. The outcome of the experiment are discussed along with an analogy leading to the idea of electrons requiring sufficient energy to escape a potential well and the corresponding equation.
A worksheet providing questions about the photoelectric effect is also linked.View Resource
These videos cover a wide range of approaches to teaching area of quantum and nuclear physics.
The “Photoelectric effect” video demonstrates the effect using an electroscope and then discusses the effect in detail using Lego to give an interesting visual approach. This can me used to explain the effect before moving on to the equation.
After the video discuss why a voltage will not assist in the escape of photoelectrons.View Resource
- Taslidere, E., () Development and use of a three-tier diagnostic test to assess high school students’ misconceptions about the photoelectric effect, Research in Science & Technological Education, 34 (2) 164–186.
- Steinburg, R., Oberem, G. and McDermott, L., () Development of a computer-based tutorial on the photoelectric effect, American Journal of Physics, 64 (11)