Wave Behaviour (Cambridge (CIE) IGCSE Physics): Revision Note

Reflection, refraction & diffraction

• All waves, whether transverse or longitudinal, can undergo:

  • reflection at a plane surface

  • refraction due to a change of speed

  • diffraction through a narrow gap

• The material a wave travels through is called a medium

  • When referring to more than one medium, these are called media

Reflection

• Reflection occurs when:

A wave hits the boundary between two media and bounces back, staying in the original medium instead of passing through

An example of reflection

Refraction

• When waves enter a different medium, their speed can change

• This effect is called refraction, and it occurs when:

A wave passes a boundary between two different media and undergoes a change in speed

• When a wave refracts, the wave undergoes:

  • a change in speed

  • a change in wavelength

  • a change in direction

  • no change in frequency

An example of refraction

• The direction of the incident and refracted rays (opens in a new tab) is also taken from the normal line

• If the waves slow down, they will bunch together, causing the wavelength to decrease

  • The waves will also start to turn slightly towards the normal

• If the waves speed up then they will spread out, causing the wavelength to increase

  • The waves will also turn slightly away from the normal

Diffraction

• When waves pass through a narrow gap, the waves spread out

• This effect is called diffraction

Waves diffracting through a narrow gap

diffracted,

Factors affecting diffraction

Extended Tier Only

• The extent of diffraction depends on the width of the gap compared with the wavelength of the waves

  • Diffraction is greatest when the wavelength of the wave is similar to (or equal to) the width of the gap

• As the gap gets bigger, the effect gradually gets less pronounced until, in the case that the gap is very much larger than the wavelength, the waves no longer spread out at all

• Diffraction can also occur when waves curve around an edge or barrier

• The waves spread out into the region behind the object

• The extent of this diffraction also depends upon the wavelength of the waves

  • The greater the wavelength, the greater the diffraction