| Lesson Plan |
| Grade: |
Date: 01/12/2025 |
| 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.
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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
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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.
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Lesson Structure:
- Do‑Now (5'): Students answer a short question on photon energy on the board.
- Mini‑lecture (10'): Derive threshold frequency and wavelength from φ = hν₀ = hc/λ₀, using the whiteboard.
- Guided practice (12'): Work through the worked example together, converting φ to joules and calculating ν₀ and λ₀.
- Simulation activity (10'): Students explore a photoelectric effect simulation, adjusting wavelength and observing electron emission.
- Conceptual check (8'): Quick quiz using clickers – three statements about intensity vs. frequency.
- Data‑table analysis (10'): Interpret the provided metal table to predict which metals will emit electrons for a given light source.
- Summary discussion (5'): Recap key formulas and answer lingering questions.
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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.
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