Wave is a transfer of energy, in the form of disturbance through some medium, without translocation of the medium. A wave having a short duration is called pulse. Waves that vibrate in repeating cycles illustrate periodic motion or harmonic motion. One complete oscillation is called cycle.

Transverse vibration occurs when vibration of the medium is perpendicular to the direction of energy transfer. The maximum and minimum positions on a transverse wave are called the crest and trough.

Longitudinal vibration occurs when the medium vibrates parallel to the direction of energy transfer. Longitudinal vibrations consist of regions of compression and rarefaction.

Frequency (f) describes the number of cycles occurring in a given unit of time. The SI unit for frequency is hertz (Hz). The units cycles / second are also used.

Frequency = Number of cycles / Time Interval

Period (T) is the time required to complete one full cycle. Period and frequency exhibit a reciprocal relationship. The amplitude of a wave is the maximum displacement from the equilibrium or the rest position.

Wavelength (l) is the distance between successive crests or successive troughs. The wavelength is the shortest distance between two points in phase (or two points that have identical characteristics). The universal wave equation (v = fl) is said to be universal because it applies to all types of waves. The universal wave equation can be used to solve various problems relating to wave motion.

Reflection of Waves. When a series of waves strikes an obstacle, the waves are reflected. Waves falling upon the barrier are called incident waves and waves reflecting from the barrier are called reflected waves. Reflection of waves can be summarized in the following law of reflection: the angle of incidence (q_i) is equal to angle of reflection (q_r). Here is a diagram illustrating the reflection of waves:

Refraction of Waves. Refraction occurs at the boundary between two different media and causes the waves to change direction as shown in the following diagram:

Diffraction of Waves. Diffraction is the bending that occurs when a wave passes around the edge of an obstacle. Waves having longer wavelengths are diffracted more than those with shorter wavelengths. When waves pass through a slit, diffraction is maximized when the wavelength and the slit width are within the same order of magnitude.