Lesson Plan

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Lesson Plan
Grade: Date: 17/01/2026
Subject: Physics
Lesson Topic: understand and use the terms threshold frequency and threshold wavelength
Learning Objective/s:
  • Describe the relationship between work function, threshold frequency and threshold wavelength.
  • Calculate threshold frequency and wavelength from a given work function.
  • Explain why photons below the threshold cannot cause photoemission regardless of intensity.
  • Apply the photoelectric equation to solve quantitative problems.
Materials Needed:
  • Projector and screen
  • Interactive whiteboard or blackboard
  • Handout with key equations and sample data table
  • Scientific calculators
  • Photoelectric effect simulation (e.g., PhET)
  • Laser pointer or LED demonstration set
 Introduction:
Begin with a quick poll: which everyday devices rely on the photoelectric effect (e.g., solar panels, light meters)? Review that photon energy is E = hν = hc/λ, linking frequency and wavelength to energy. State that by the end of the lesson students will be able to determine whether a light source can liberate electrons from a metal using the concepts of threshold frequency and wavelength.
Lesson Structure:
  1. Do‑Now (5'): Students answer a short question on photon energy on the board.
  2. Mini‑lecture (10'): Derive threshold frequency and wavelength from φ = hν₀ = hc/λ₀, using the whiteboard.
  3. Guided practice (12'): Work through the worked example together, converting φ to joules and calculating ν₀ and λ₀.
  4. Simulation activity (10'): Students explore a photoelectric effect simulation, adjusting wavelength and observing electron emission.
  5. Conceptual check (8'): Quick quiz using clickers – three statements about intensity vs. frequency.
  6. Data‑table analysis (10'): Interpret the provided metal table to predict which metals will emit electrons for a given light source.
  7. Summary discussion (5'): Recap key formulas and answer lingering questions.
Conclusion:
Summarise that the threshold conditions stem directly from the work function and dictate the minimum photon energy required. Ask each student to write one exit‑ticket sentence stating the formula for λ₀ and an example metal where λ₀ ≈ 500 nm. Assign homework: complete a worksheet converting various work functions to threshold frequencies and wavelengths.