Waves Terms

Wave

A periodic disturbance that transfers energy without transferring matter.

–

–

–

Oscillation

A repeated back-and-forth motion about an equilibrium position.

–

–

–

Vibration

A form of oscillation in a particle or system.

–

–

–

Medium

The material through which a mechanical wave travels.

–

–

–

Wavefront

A line joining points on a wave that are in phase.

–

–

–

Ray

A line showing the direction of energy propagation, perpendicular to the wavefronts.

–

–

–

Mechanical wave

A wave that requires a medium for propagation.

–

–

–

Electromagnetic wave

A wave consisting of oscillating electric and magnetic fields that can propagate through a vacuum.

–

–

–

Transverse wave

A wave in which particles of the medium oscillate perpendicular to the direction of propagation.

–

–

–

Longitudinal wave

A wave in which particles of the medium oscillate parallel to the direction of propagation.

–

–

–

Compression

A region in a longitudinal wave where particles are closest together (high pressure).

–

–

–

Rarefaction

A region in a longitudinal wave where particles are furthest apart (low pressure).

–

–

–

Displacement

Distance of a particle from its equilibrium position at any given time.

xx

m (metre)

–

Amplitude

Maximum displacement of a particle from its equilibrium position.

AA

m (metre)

–

Cycle

One complete oscillation or vibration.

–

–

–

Period

The time taken for one complete cycle of oscillation.

TT

s (second)

T=1fT = \frac{1}{f}

Frequency

The number of complete oscillations per second.

ff

Hz (s⁻¹)

f=1Tf = \frac{1}{T}

Wavelength

The distance between two consecutive points in phase on a wave.

λ\lambda

m (metre)

–

Wave speed

The distance travelled by the wave per unit time.

vv

m·s⁻¹

v=fλv = f \lambda

Phase

The position and motion of a particle relative to others at a specific instant, expressed as an angle.

ϕ\phi

degrees (°) or radians (rad)

–

Phase difference

The difference in phase between two points on a wave.

–

° or rad

–

Reflection

The change in direction of a wave when it bounces off a surface.

–

–

θi=θr\theta_i = \theta_r

Refraction

The bending of a wave as it passes from one medium to another, due to a change in speed.

–

–

n1sin⁡θ1=n2sin⁡θ2n_1 \sin \theta_1 = n_2 \sin \theta_2

Diffraction

The spreading of a wave as it passes around an obstacle or through an aperture.

–

–

–

Superposition

When two or more waves overlap, the resultant displacement is the algebraic sum of individual displacements.

–

–

–

Standing wave

A stationary wave formed by the interference of two waves of the same frequency travelling in opposite directions.

–

–

–

Resonance

A phenomenon in which an object oscillates with large amplitude when driven at its natural frequency.

–

–

–

Sound intensity

The power carried by a sound wave per unit area perpendicular to the direction of propagation.

II

W·m⁻²

I=PAI = \frac{P}{A}

Sound level

A logarithmic measure of sound intensity, expressed in decibels.

LL

dB

L=10log⁡II0L = 10 \log \frac{I}{I_0}

Quality (timbre)

The characteristic tone of a sound, determined by the presence and relative strength of harmonics.

–

–

–

Pitch

The perceived frequency of a sound.

–

–

–

Refractive index

The ratio of the speed of light in a vacuum to its speed in a medium.

nn

–

n=cvn = \frac{c}{v}

Critical angle

The angle of incidence beyond which total internal reflection occurs.

–

° (degree)

sin⁡θc=n2n1\sin \theta_c = \frac{n_2}{n_1}

Total internal reflection (TIR)

Reflection of a wave within a medium when it strikes the boundary at an angle greater than the critical angle.

–

–

–

Dispersion

The splitting of white light into its component colours due to wavelength-dependent refraction.

–

–

–