4.4c Diffraction

THE IB SAYS

Essential idea: Waves interact with media and each other in a number of ways that can be unexpected and useful.

Understandings: Diffraction through a single-slit and around objects

Applications and skills: Qualitatively describing the diffraction pattern formed when plane waves are incident normally on a single-slit

Guidance: Students should have the opportunity to observe diffraction and interference patterns arising from more than one type of wave

My vodcast

Diffraction

Diffraction is one of the standard wave phenomena that all two or three dimension waves can experience. It occurs when waves pass through a slit or past the edge (or edges) of an object.

A (semi) circular diffraction pattern occurs when the width of the slit is approximately the same size as the wavelength of the wave.

Huygens's principle / construction provides a good explanation of how and why diffraction occurs.

Diffraction of light by a narrow slit

When a coherent monochromatic light source passes through a narrow slit then it will produce a diffraction pattern on a screen placed at an appropriate distance. Note that for SL Wave Behaviour only a qualitative description is required. A more mathematical description is expected as part of the AHL topic 9. Wave Phenomena.

Extra videos

Simulations

Walter Fendt simulation

Resources from textbooks

Oxford Physics: pages 151 - 152

Hamper HL (2014): pages 189 - 191, but includes a HL-oriented mathematical approach

Relevant questions from Dot Point Physics (4 Oscillations and Waves)

pages 210 - 213

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