Interference is a fundamental phenomenon in wave physics. When two or more waves meet at the same point in space, they combine according to the principle of superposition. This means their amplitudes simply add together algebraically. The resulting wave pattern depends on how the individual waves align with each other.
Constructive interference happens when two waves meet in phase, meaning their crests align with crests and troughs align with troughs. When this occurs, the amplitudes of the waves add together, resulting in a combined wave with greater amplitude than either individual wave. This leads to increased intensity, such as brighter light or louder sound.
Destructive interference occurs when two waves meet out of phase, meaning the crest of one wave aligns with the trough of another. In this case, the amplitudes subtract from each other. When two waves of equal amplitude are perfectly out of phase, they completely cancel each other out, resulting in zero amplitude. This can create areas of silence in sound waves or darkness in light waves.
In real-world situations, waves often have different amplitudes or phase relationships that are neither perfectly in phase nor perfectly out of phase. This creates partial interference, where the resulting wave has an amplitude somewhere between complete constructive and complete destructive interference. The exact pattern depends on the specific amplitude and phase differences between the interfering waves.
For interference to create stable, predictable patterns, the waves must be coherent. This means they have the same frequency and maintain a constant phase relationship over time. Coherent interference is essential in many technologies including laser systems, noise-canceling headphones, and precision optical instruments like interferometers used in scientific research.