Lesson Plan

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Lesson Plan
Grade: Date: 17/01/2026
Subject: Physics
Lesson Topic: understand that a photon has momentum and that the momentum is given by p = E / c
Learning Objective/s:
  • Describe how a photon’s energy relates to its frequency and wavelength.
  • Explain why a mass‑less photon still possesses momentum and derive the relation p = E/c.
  • Apply the momentum formula to calculate photon momentum for various wavelengths and determine radiation pressure.
  • Analyse real‑world applications such as solar sails and laser‑induced forces.
Materials Needed:
  • Projector and laptop for slides
  • Laser pointer with lightweight suspended mirror
  • Ruler or measuring stand
  • Scientific calculators
  • Worksheet with practice problems
  • Printed diagram of photon momentum transfer
 Introduction:
Begin with a quick demonstration of a laser pointer pushing a tiny suspended mirror, prompting curiosity about how light can exert a force. Recall that students already know the photon energy formula E = hν and the concept of radiation pressure. Today they will determine how that energy translates into momentum using p = E/c and apply it to real‑world scenarios. Success will be measured by correctly deriving the formula and solving quantitative problems.
Lesson Structure:
  1. Do‑now (5') – Short quiz on photon energy (E = hν) and wave‑particle duality.
  2. Mini‑lecture (10') – Derive p = E/c from the relativistic relation and show p = h/λ using slides.
  3. Demonstration (8') – Laser pointer on suspended mirror; discuss observed motion and link to radiation pressure.
  4. Guided practice (12') – Work through the 500 nm example and table values; students calculate momentum and pressure in pairs.
  5. Application activity (10') – Problem: compute thrust on a solar sail at 1 AU; groups present results.
  6. Misconception check (5') – Quick poll on why photons have momentum despite zero mass; teacher clarifies.
  7. Exit ticket (5') – One‑sentence answer: state the momentum formula and give a real‑world example.
Conclusion:
Summarise that photons, though massless, carry momentum given by p = E/c, which underlies radiation pressure and technologies like solar sails. Students have demonstrated this through calculations and a laser demonstration. For homework, assign a worksheet where they calculate photon momentum for ultraviolet and X‑ray wavelengths and estimate the force on a spacecraft sail. Collect exit tickets to assess immediate understanding.