The Photoelectric Effect

Contact Information:

  • Tamala Sebring. Email:


The Photoelectric Effect is an important phenomenon in physics as well as in everyday life.  Einstein was not the first to observe the Photoelectric Effect but he was the first to explain it and his 1905 paper earned him the 1921 Nobel Prize in Physics.  Understanding the Photoelectric Effect not only helps us understand the dual wave and particle nature of light, it also allows us to change light into electricity for use in many common objects.  Students will explore and expand their understanding of this phenomenon by using an online simulation, engaging in a role-play activity, and researching several common objects such as solar panels, digital cameras, and night vision goggles.  The unit will culminate in an explanation of how the Photoelectric Effect works in photomultiplier tubes that are used to detect low intensity light given off by gamma ray and cosmic ray interactions with particles in the Earth’s atmosphere.

Lesson Content Overview:

  • Engage (45 min):  Students will view a slide that contains several common objects and will be asked to identify what they all have in common (they each take light and change it into electricity). After a brief class discussion, students will be asked if light can have any effect on a charged electroscope.  The class will then view a demonstration (either live or on video) of white, red, blue, UV-A, and UV-C light being shined on a charged electroscope and only the UV-C light will make the electroscope discharge.
  • Explore (45 min):  Students will use an online simulation to determine what effect light intensity, light wavelength, target metal type, and battery voltage might have on the electrons that are emitted from the target metal.  This is a guided activity that has several open-ended questions at the end to allow students to come to their own conclusions.  After the simulation activity, the class will revisit the observations from the electroscope demonstration to try to put it into perspective.
  • Explain (45 min):  Students will participate in a role-play activity where some of the students will be the target metal (white pom poms will be used for electrons) and other students will be the incident light (colored pom poms will be used for the photons, each color will represent a certain wavelength).  The role-play activity will help to clarify and deepen the students’ understanding of how the intensity and wavelength of the incident light affects electron emission.  Notes will be given after each part of the activity.  Additional notes are included that detail the equation and how we came to understand that light can behave as both wave and particle.
  • Elaborate / Evaluate (90 min):  During this part of the unit, students will be divided into groups and assigned a type of photocell to research – solar cells, digital cameras, photosensors, night vision goggles, and photomultiplier tubes.  Each group will find how their particular photocell takes light and changes it into electricity.  Each group will then report their findings to the class.
  • Extend (45 min):  A presentation will show how photomultiplier tubes are used to detect low intensity light that is produced when gamma rays and cosmic rays interact with particles in the atmosphere.  This presentation focuses on the HAWC Gamma-ray Observatory and how gamma ray and cosmic ray air showers produce Cherenkov light in the water tanks.  This light can then be detected by the photomultiplier tubes and turned into data that can be used to determine the origin of the gamma rays.

Supporting Material:

The Photoelectric Effect – Lesson Details

Photoelectric Effect Classroom Presentation

Electroscope Demonstration – YouTube

PhET Sim Photoelectric Effect Student Activity

PhET Sim Photoelectric Effect ANSWERS

Physics Aviary Sim Photoelectric Effect Student Activity

Physics Aviary Sim Photoelectric Effect ANSWERS

Elaborate Assignments – How the Photoelectric Effect is Used Student Activity

Elaborate Assignments – How the Photoelectric Effect is Used ANSWERS