Lesson 4: Wave-Particle Duality & De Broglie Wavelength
Demonstrating understanding of quantum phenomena, atomic structures, nuclear reactions, and special relativity.
🎯 Ngā Whāinga Akoranga | Learning Intentions
Wave-particle duality of light and matter, De Broglie hypothesis λ = h / p = h / (m v), electron diffraction (Davisson-Germer experiment), and matter wave implications.
Calculate De Broglie wavelength for macroscopic vs subatomic particles, analyse electron microscope resolution advantage, and explain double-slit interference of single electrons.
🎥 Media Anchor & Pedagogical Scaffold
De Broglie Matter Waves & Quantum Duality
Video Clip: De Broglie wavelength — matter waves, λ = h/mv, and wave-particle duality | Khan Academy Physics (Runtime: 11m 20s).
🧠 1. Before Viewing (Activate & Predict)
If light waves behave like particles, can solid particles like electrons also behave like spreading waves?
👁️ 2. During Viewing (Watch With a Job)
- De Broglie hypothesis: what did de Broglie propose about matter? Write the de Broglie equation λ = h/mv and identify all variables and their units.
- Calculate: an electron has mass 9.11 × 10⁻³¹ kg and moves at 2 × 10⁶ m/s. Calculate its de Broglie wavelength. Is this wavelength visible?
- Significance: why does wave-particle duality matter? Give ONE real-world application of electron wave behaviour (the video mentions at least one).
🗣️ 3. After Viewing & Kaiako Move (Process & Apply)
Kaiako Move: Show double-slit electron interference video clips demonstrating single electrons building interference fringes over time.
Immediate Task: Complete Section 4 of your Physics Portfolio: De Broglie Wavelength Problem Set & Quantum Duality Essay.
⚡ Whakaoho | Do Now: Modern Physics Recall (10 mins)
You have a wavelength right now. De Broglie's hypothesis applies to everything with momentum, including you walking through a doorway.
Two minutes: estimate your mass and walking speed, then calculate λ = h/mv. Look at the number. Now say why nobody has ever observed a person diffracting through a doorway — the reason is in the size of what you just calculated compared with the door.
📖 Activity 1: Physics Concept Exploration & Problem Solving (25 mins)
Two extremes (15 min). Calculate the de Broglie wavelength of (a) a cricket ball at 30 m s⁻¹ and (b) an electron accelerated through 100 V. Compare each with something of similar size — an atom, a nucleus, a doorway. Then state the general rule for when wave behaviour becomes observable.
The evidence (10 min). Davisson and Germer fired electrons at a nickel crystal and got a diffraction pattern. Explain why that result is impossible for particles and expected for waves, and what it therefore proves about matter.
📝 Activity 2: Level 3 Physics Portfolio Task & Merit/Excellence Scaffolding (20 mins)
Portfolio — Section 4. Submit: (1) your own de Broglie wavelength with working, and the reason you do not diffract; (2) both extreme calculations with size comparisons; (3) a paragraph on Davisson–Germer explaining what the diffraction pattern rules out.
🏫 Kaiako Planning & Pedagogy Notes
NCEA Level 3 Alignment: Direct preparation for Level 3 Physics (Demonstrate understanding of application of modern physics). Emphasise clear physical explanations and multi-step mathematical working for Merit/Excellence grades.