Wave, propagation of disturbances from place to place in a regular and organized way. Most familiar are surface waves that travel on water, but sound, light, and the motion of subatomic particles all exhibit wavelike properties. In the simplest waves, the disturbance oscillates periodically (see periodic motion) with a fixed frequency and wavelength. Mechanical waves, such as sound, require a medium through which to travel, while electromagnetic waves (see electromagnetic radiation) do not require a medium and can be propagated through a vacuum. Propagation of a wave through a medium depends on the medium’s properties. See also seismic wave.
waveA wave in water.
Types And Features Of Waves
Waves come in two kinds, longitudinal and transverse. Transverse waves are like those on water, with the surface going up and down, and longitudinal waves are like of those of sound, consisting of alternating compressions and rarefactions in a medium. The high point of a transverse wave is a called the crest, and the low point is called the trough. For longitudinal waves, the compressions and rarefactions are analogous to the crests and troughs of transverse waves. The distance between successive crests or troughs is called the wavelength. The height of a wave is the amplitude. How many crests or troughs pass a specific point during a unit of time is called the frequency. The velocity of a wave can be expressed as the wavelength multiplied by the frequency.
Waves can travel immense distances even though the oscillation at one point is very small. For example, a thunderclap can be heard kilometres away, yet the sound carried manifests itself at any point only as minute compressions and rarefactions of the air.
Wave Behaviour
Waves display several basic phenomena. In reflection, a wave encounters an obstacle and is reflected back. In refraction, a wave bends when it enters a medium through which it has a different speed. In diffraction, waves bend when they pass around small obstacles and spread out when they pass through small openings. In interference, when two waves meet, they can interfere constructively, creating a wave with larger amplitude than the original waves, or destructively, creating a wave with a smaller (or even zero) amplitude.
Reflection
When waves hit a boundary and are reflected, the angle of incidence equals the angle of reflection. The angle of incidence is the angle between the direction of motion of the wave and a line drawn perpendicular to the reflecting boundary.
Refraction
The speed of a wave depends on the properties of the medium through which it travels. For example, sound travels much faster through water than through air. When a wave enters at an angle a medium through which its speed would be slower, the wave is bent toward the perpendicular. When a wave enters at an angle a medium in which its speed would be increased, the opposite effect happens. With light, this change can be expressed by using Snell’s law of refraction.
Diffraction
When a wave encounters a small obstacle or a small opening (that is, small compared with the wavelength of the wave), the wave can bend around the obstacle or pass through the opening and then spread out. This bending or spreading out is called diffraction.
Interference
The waves from two or more centres of disturbance may reinforce each other in some directions and cancel in others. This phenomenon is called the interference of waves. It is easy to see how this may happen. Consider two sources producing waves of the same wavelength and in phase; that is, at their origin the crests of the waves occur at the same time. If a point P is equidistant from both sources, the crests arrive at P simultaneously and reinforce each other. Similarly, the troughs arrive simultaneously and become deeper. The same situation occurs if the distances to point P are unequal but differ by one or more full wavelengths. If, however, the distances differ by half a wavelength or by an odd number of half wavelengths, then the crests of one wave will coincide with the troughs of the other and the intensity of the resultant wave is decreased. When two such waves are of equal intensity, they will cancel each other completely. Intermediate situations arise in those directions in which the distances traveled by the two waves differ by some other fraction of a wavelength, the waves tending either to reinforce or to cancel each other.
examples of interferenceWhen two waves of identical wavelength are in phase, they form a new wave with an amplitude equal to the sum of their individual amplitudes (constructive interference). When two waves are of completely opposite phase, they either form a new wave of reduced amplitude (partial destructive interference) or cancel each other out (complete destructive interference). Much more complicated constructive and destructive interference patterns emerge when waves with different wavelengths interact.
