3.1.4Waves
Wave Behaviour — Cambridge IGCSE Co-ordinated Sciences 0654 - Physics Revision Notes & Topical Questions
5 min read 10 parts Lesson 5 of 21
Part 1 of 8Wave behaviours and media
All waves
- All waves transverse and longitudinal waves can be reflected at a plane surface, refracted when speed changes and diffracted through a narrow gap
Medium
- Medium the material a wave travels through, and several are called media
Part 2 of 8Reflection
Reflection
- Reflection a wave hits the boundary between two media and bounces back into the original medium
Law of reflection
- Law of reflection angle of incidence equals angle of reflection, both measured from the normal
- The incident ray, reflected ray and normal lie in the same plane
Unchanged
- Unchanged wavelength, frequency and speed
Everyday
- Everyday echoes are reflected sound and mirrors reflect light
Part 3 of 8Refraction
Refraction
- Refraction a wave passing a boundary between two media changes speed
Changes
- Changes speed, wavelength and direction change but frequency does not
Slowing down
- Slowing down the waves bunch together, the wavelength decreases and they turn slightly towards the normal
Speeding up
- Speeding up the waves spread out, the wavelength increases and they turn slightly away from the normal
Along the normal
- Along the normal the speed changes but the direction does not
Cause
- Cause refraction is the change in speed and the change in direction is a consequence
Part 4 of 8Diffraction
Diffraction
- Diffraction waves spread out when they pass through a narrow gap or past an edge
Unchanged
- Unchanged wavelength, frequency and speed stay the same, so wavefronts keep the same spacing
Gap size
- Diffraction is greatest when the wavelength is similar to the gap width
- A gap much larger than the wavelength gives almost no spreading
- A very narrow gap lets little energy through
Edges
- Edges waves curve around an edge or barrier into the region behind
- Longer wavelengths diffract more
- Shorter wavelengths diffract less
Part 5 of 8Everyday evidence
Sound round corners
- Sound round corners sound wavelengths of about 0.1 to 3 m are comparable to doorways, so they diffract strongly
Light
- Light visible light has a wavelength of about 5 × 10−7 m and hardly diffracts
Radio
- Radio long-wavelength radio waves bend over hills and short-wavelength signals need line of sight
Harbour
- Harbour water waves curve around a harbour wall and spread into the harbour
Part 6 of 8What changes
| Behaviour | Speed | Wavelength | Frequency | Direction |
|---|---|---|---|---|
| Reflection | Same | Same | Same | Changes |
| Refraction (slower medium) | Decreases | Decreases | Same | Towards the normal |
| Diffraction | Same | Same | Same | Spreads out |
Part 7 of 8Drawing wavefronts
Reflection
- Reflection keep the wavelength the same and make the angle of incidence equal the angle of reflection
Refraction
- Refraction wavefronts closer together in the slower region
Diffraction
- Diffraction straight wavefronts approaching a gap,
- and for a gap similar to the wavelength semi-circular crests centred on the gap with unchanged spacing
Refraction only
- Refraction only the only wave effect in which wavelength changes
Depth change
- Depth change a change of direction at a depth boundary is refraction, diffraction happens at a gap or an edge
Part 8 of 8More from the specification
More from the specification
Wave behaviour in ripple tanks
- Water waves in a ripple tank demonstrate reflection from barriers, refraction caused by changes in water depth,
- and diffraction through gaps.
Wavefronts and ray direction
- A wavefront connects adjacent points oscillating in phase;
- wave rays indicate the perpendicular direction of wave propagation and energy transfer.
Diffraction dependency on aperture size
- Wave diffraction is most pronounced when the width of an aperture is comparable to or smaller than the wavelength of the incident wave.
Ripple
- The small fluctuation left in the smoothed output
Amplitude
- Maximum displacement from equilibrium.
Distance
- Total length of path travelled, a scalar.
Position
- Location relative to a reference point.
Trough
- The lowest point of a wave.
Period
- Time for one revolution.
Key terms
| Term | Meaning |
|---|---|
| Reflection | Wave bouncing back at a boundary into the original medium |
| Refraction | Change of speed of a wave at a boundary between media |
| Diffraction | Spreading of waves through a gap or around an edge |
| Normal | Line at right angles to a boundary |
| Medium | Material through which a wave travels |
Avoid these mistakes
1
Saying the wavelength changes in diffraction — it stays the same.
2
Saying frequency changes in refraction — it stays the same.
3
Drawing reflected waves with a different angle from incidence — the angles must be equal.
4
Calling a change of direction at a depth boundary diffraction — that is refraction.
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