(455) HL Evidence of wave or particle behaviour [IB Physics HL]

Introduction to Light

• Light is a common daily experience, raising the question: "What is light?"

• We explore the nature of light using models, often comparing it to particles or waves.

Light as a Particle

• Particle Properties:

  • Reflects off surfaces (e.g., bouncing off walls).

  • Transfers momentum (pushes other objects).

  • Can refract (change speed and angle in different materials).

    • Example: Apparent bending of an arm underwater due to refraction.

• Photoelectric Effect:

  • Demonstrates light's particle nature as photons can eject electrons from metal surfaces (e.g., zinc).

  • Light shows sufficient localization of energy, which waves cannot.

Light as a Wave

• Wave Properties:

  • Can also reflect and refract when interacting with surfaces.

  • Diffraction:

    • Light spreads out and creates patterns of bright and dark spots due to interference.

    • Constructive and destructive interference explains this behavior; particles cannot interfere.

• Conclusion from Diffraction:

  • Suggests light must be a wave, contradicting the previous conclusion of it being a particle.

The Duality of Light

• Conflict arises between findings from the photoelectric effect (light as a particle) and diffraction (light as a wave).

• Current understanding concludes: light exhibits both particle and wave behaviors.

• Photon Concept:

  • Proposed as the fundamental particle of light, embodying both wave and particle characteristics.

• Einstein’s Perspective:

  • Suggested not forcing light into just one classification; it can exist as its unique entity.

Implications for Matter

• Similar duality observed in matter, with particles like electrons also demonstrating wave behavior.

• This phenomenon is known as wave-particle duality and highlights the complex nature of light and matter.