| English | Interference |
|---|---|
| Bahasa Melayu | Interferens |
| 中文 | 干涉 |
Definition
The superposition of two waves of the same type, producing regions of reinforcement (constructive) and cancellation (destructive).
In exam terms
Interference is the superposition of two waves of the same type travelling in the same region, producing points of reinforcement (constructive) and points of cancellation (destructive).
Constructive interference occurs where a crest meets a crest (or a compression meets a compression), giving a larger amplitude. Destructive interference occurs where a crest meets a trough, giving zero or reduced amplitude. For a clear, steady pattern the two sources must be coherent, same frequency and a constant phase difference.
In the double-slit pattern the fringe separation is given by λ = ax ÷ D, where a is slit separation, x is fringe spacing and D is the distance to the screen.
Do not confuse it with diffraction
Interference needs two (or more) waves overlapping, giving alternating bright and dark or loud and soft regions. Diffraction is a single wave spreading through a gap or round an obstacle. In practice diffraction sets up the overlapping waves that then interfere, but the definitions are distinct: interference is about superposition, diffraction is about spreading.
In Paper 2 you may be asked to state the conditions for a clear interference pattern (coherent sources) or to calculate a quantity using λ = ax ÷ D. Keep all lengths in metres so the wavelength comes out in metres.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)