Lesson Plan: The Kinetic Energy of Photoelectrons Physics • 9th Grade

This lesson plan includes the objectives, prerequisites, and exclusions of the lesson teaching students how to calculate the maximum possible kinetic energy of electrons that are ejected from the surface of a material due to the photoelectric effect.

Objectives

Students will be able to

  • describe what the photoelectric effect is,
  • use the formula 𝐸=𝑓𝑊max
    • to find the maximum kinetic energy, 𝐸max, of electrons emitted from a material via the photoelectric effect given the other values,
    • to find the frequency, 𝑓, of photons incident on the surface of the material given the other values,
    • to find the work function, 𝑊, of the material given the other values,
  • work out the work function of a material from a graph of electron kinetic energy against photon frequency,
  • work out the work function of a material from a graph of electron kinetic energy against photon wavelength.

Prerequisites

Students should already be familiar with

  • the idea that light consists of photons,
  • how to use the formulas 𝐸=𝑓 and 𝐸=𝑐𝜆,
  • how to convert between electronvolts (eV) and joules (J),
  • how to use the formula 𝐸=12𝑚𝑣 to find the kinetic energy of an object with mass 𝑚 and speed 𝑣,
  • how to use the formula 𝐼=𝑄𝑡 to find the current if a total charge 𝑄 moves past a point in an amount of time 𝑡.

Exclusions

Students will not cover

  • the concept that photons have momentum or calculating the momentum of a photon given its frequency or wavelength,
  • other particle-like behavior of light, such as Compton scattering,
  • the idea that when an atom absorbs a photon, one of the electrons in the atom moves to a higher energy level and that when an atom emits a photon, one of the electrons in the atom moves to a lower energy level.
  • the factors that cause one material to have a higher or lower work function than another.

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