Teacher Notes & Alignment
Performance Expectation: HS-PS4-3: Evaluate the claims, evidence, and reasoning behind the idea that electromagnetic radiation can be described either by a wave model or a particle model, and that for some situations one model is more useful than the other.
Anchoring Phenomenon: Light can behave in seemingly contradictory ways depending on the experiment. When light passes through narrow slits, it creates an interference pattern (like ripples in water). However, when light shines on a metal plate, it can eject electrons as discrete packets (photons) only if the wavelength is short enough (which means high enough frequency and energy), regardless of intensity.
Science and Engineering Practices (SEPs):
- Engaging in Argument from Evidence: Students evaluate the claims, evidence, and reasoning behind currently accepted explanations.
Disciplinary Core Ideas (DCIs):
- PS4.B: Electromagnetic Radiation: Electromagnetic radiation can be modeled as a wave of changing electric and magnetic fields or as particles called photons.
Crosscutting Concepts (CCCs):
- Systems and System Models: Models can be used to simulate systems and interactions.
Evidence Statements Addressed:
- Identifying claims, evidence, and reasoning: Students identify that light acts as a wave (interference pattern in double slit) and a particle (photoelectric effect).
- Evaluating given evidence and reasoning: Students evaluate how interference supports the wave model and how the photoelectric effect supports the particle model, reasoning why each model is useful for different phenomena.
Task Details
Estimated Time: 45–60 minutes Materials Needed: Access to the Wave-Particle Duality of Light simulation, student handout, calculator (optional).
Engage
Look at the two different models of light presented in the simulation. Have you ever wondered if light is a wave (like a wave in the ocean) or a particle (like a tiny ball)? Over centuries, scientists debated this. Discuss with a partner: what behavior of light makes you think it is a wave? What behavior makes you think it is a particle?
Explore
Open the simulation and perform the following investigations:
Part 1: The Wave Model (Double Slit Experiment)
- Select the Wave Model tab.
- Observe the light passing through the two slits.
- Adjust the Slit Spacing slider to “Narrow”, “Medium”, and “Wide”.
- Record your observations of the interference pattern on the back wall. How does the pattern change when the slits are closer together versus further apart?
Sample Data Table 1: Wave Model Observations
| Slit Spacing | Observations of Interference Pattern |
|---|---|
| Narrow | _________ |
| Medium | _________ |
| Wide | _________ |
Part 2: The Particle Model (Photoelectric Effect)
- Select the Particle Model tab.
- The simulation displays a metal plate with a threshold wavelength of ~500 nm.
- Adjust the Wavelength (Color) slider from 700 nm (Red) down towards the blue/violet spectrum (< 500 nm).
- Note what happens when the photons hit the metal plate at different wavelengths.
Sample Data Table 2: Particle Model Observations
| Wavelength (nm) | Color | Are electrons ejected? | Observations of electron speed (Kinetic Energy) |
|---|---|---|---|
| 700 nm | Red | ____ | _________ |
| 600 nm | Yellow/Orange | ____ | _________ |
| 500 nm | Green/Cyan | ____ | _________ |
| 400 nm | Violet | ____ | _________ |
Explain
- Wave Model: Based on Part 1, how does the interference pattern support the claim that light travels as a wave? Explain the bright and dark spots in terms of constructive and destructive interference.
- Particle Model: Based on Part 2, how does the photoelectric effect support the claim that light consists of particles (photons)? Explain why light above 500 nm does not eject electrons, while light below 500 nm does. Use the equation for photon energy $E = \frac{hc}{\lambda}$ (or $E = hf$) to support your reasoning.
- Duality: Why is it necessary to have both models to fully describe the behavior of electromagnetic radiation?
Elaborate
Investigate how different metals have different work functions. If a new metal plate had a threshold wavelength of 400 nm, how would the results in Part 2 change? Design a brief hypothetical experiment to test this. How does this demonstrate the idea that scientific theories are modified in light of new evidence?
Evaluate
Student Deliverable: Write a short scientific argument consisting of a claim, evidence, and reasoning (CER).
- Claim: State that light exhibits both wave-like and particle-like properties depending on the experiment.
- Evidence: Cite specific observations from your data tables (e.g., the interference pattern for wave properties, the threshold wavelength for the photoelectric effect).
- Reasoning: Connect your evidence to the concepts of wave interference and discrete photon energy packets ($E = hf$). Explain why neither model alone is sufficient to explain both phenomena.