Physics - Wave-Particle Duality

OCR A-Level Physics 2022


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Flashcards

Evidence for wave and particle behaviour

What’s the evidence that light exists as a particle?

The photoelectric effect.

What’s the evidence that light exists as a wave?

They form diffraction patterns.

What’s the evidence that electrons exist as a wave?

They form diffraction patterns.

The electron two-slit experiment

What would you expect when firing electrons through two slits if they are a particle?

There should be two bright spots and no interference pattern.

What do you get when you fire electrons through two slits?

An interference pattern.

What three pieces of equipment do you need to use to demonstrate electrons can act like waves?

  • Electron gun
  • Thin graphite grating
  • Luminescent screen

Fringe spacing and the de Broglie wavelength

What happens for the fringe spacing in a diffraction pattern created by fast-moving electrons?

It is small.

What happens for the fringe spacing in a diffraction pattern created by slow-moving electrons?

It is large.

What is the formula for the de Broglie wavelength $\lambda$ of a particle with mass $m$ and velocity $v$?

\[\lambda = \frac{h}{mv}\]

What’s another way of thinking about the de Broglie wavelength in terms of momentum?

\[\lambda = \frac{h}{\text{momentum}}\]