Wave and Particle Models of Light
Aligned to HS-PS4-3 — Next Generation Science Standards.
What this lesson teaches
Light behaves as a wave in some experiments and as a stream of particles (photons) in others. Interference and diffraction need the wave model, while the photoelectric effect, where light knocks electrons off a metal, needs the particle model. Scientists choose the model that fits the situation.
Worked example
Shine dim red light on a metal and no electrons escape, no matter how long you wait; switch to dim blue light and electrons pop out instantly. A wave should build up enough energy over time, so this only makes sense if each photon carries energy E = hf, and only the higher-frequency blue photons have enough.
Practice questions
- Name one phenomenon best explained by the wave model and one best explained by the particle model.
- Explain why increasing the brightness of red light still fails to eject electrons, using the photon idea.
- Evaluate the claim that light is 'only a wave,' citing evidence for both models and stating when each is used.
Watch the lesson
Every lesson comes with a video taught in English and Spanish — the same video the QR code in the printed workbook opens.
▶ Watch this lessonEn español
Modelos de Onda y de Partícula de la Luz
La luz se comporta como onda en algunos experimentos y como un flujo de partículas (fotones) en otros. La interferencia y la difracción requieren el modelo ondulatorio, mientras que el efecto fotoeléctrico, donde la luz arranca electrones de un metal, requiere el modelo de partícula. Los científicos eligen el modelo que se ajusta a la situación.
Ejemplo: Ilumina un metal con luz roja tenue y no escapa ningún electrón, sin importar cuánto esperes; cambia a luz azul tenue y los electrones salen al instante. Una onda debería acumular suficiente energía con el tiempo, así que esto solo tiene sentido si cada fotón lleva energía E = hf, y solo los fotones azules, de mayor frecuencia, tienen la suficiente.
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