| English | Diffraction |
|---|---|
| Bahasa Melayu | Pembelauan |
| 中文 | 衍射 |
Definition
The spreading of waves as they pass through a gap or around the edge of an obstacle.
In exam terms
Diffraction is the spreading of waves as they pass through a gap or around the edge of an obstacle. It is a property of all waves, including water waves, sound and light.
The amount of spreading is greatest when the gap size is about equal to the wavelength: a narrow gap or a long wavelength gives more spreading. During diffraction the frequency, wavelength and speed all stay the same; only the shape of the wavefronts and the amplitude change (the amplitude decreases because the energy spreads over a wider area).
This is why you can hear someone around a corner even when you cannot see them.
Do not confuse it with refraction
Diffraction happens within one medium as waves spread through a gap or past an edge, and the wavelength stays the same. Refraction happens when waves cross into a new medium, changing speed and wavelength. The key test: if the wavelength is unchanged and the wave is bending round an edge, it is diffraction.
In Paper 2 you may be asked to state what affects diffraction, or to draw the diffracted wavefronts after a gap. Show curved wavefronts spreading out, with the wavelength kept the same as before the gap, and note that a narrower gap spreads them more.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)