Opus in profectus
The Nature of Waves
is a disturbance that propagates through a medium.
describes the spreading of a disturbance.
Waves transfer energy, momentum, and information, but not mass.
Classifying waves by medium
Matter is the medium.
Sound is a mechanical wave.
Electric and magnetic fields are the media.
Light is an electromagnetic wave.
The gravitational field is the medium.
The existence of gravitational waves has not yet been confirmed.
Classifying waves by orientation
The disturbance is perpendicular to the direction of propagation.
All electromagnetic waves are transverse. This includes light.
is a point of maximal change in the positive direction.
is a point of maximal change in the negative direction.
The disturbance is parallel to the direction of propagation.
Sound is a longitudinal wave.
is a region where the medium is under compression.
is a region where the medium is under tension.
A combination transverse–longitudinal wave that forms near the surface of some media.
Deep water waves are surface waves.
The disturbance causes the medium to twist.
Classifying waves by duration
The disturbance is momentary and sudden.
The disturbance repeats at regular intervals.
Classifying waves by appearance
Appear to move.
Do not appear to move.
Characteristics of periodic waves
The maximum absolute value of a periodically varying quantity.
Amplitude has the unit of the quantity that is changing (ex. displacement, pressure, field strength, etc.)
The time between successive cycles of a repeating sequence of events.
(time per number of cycles)
The SI unit of period is the
The number of cycles of a repeating sequence of events in a unit interval of time.
(number of cycles per time)
Frequency and period are reciprocals (or inverses) of one another:
ƒ = 1/
The SI unit of frequency is the
[Hz = 1/s = s
The stage of development of a periodic process.
Two points on a wave with the same phase have the same…
quantity of disturbance (ex. displacement) and
rate of change of disturbance (ex. velocity).
Phase is an angular quantity.
are separated by one complete cycle.
out of phase
are separated by half a cycle.
The SI unit of phase is the
, which is itself a unitless ratio [rad = m/m = Pa/Pa = (V/m)/(V/m) = etc.].
The distance between any point on a periodic wave and the next nearest point corresponding to the same portion of the wave.
Wavelength is measured between adjacent points in phase.
The SI unit of wavelength is the
Waves propagate with a finite speed (sometimes called the wave speed) that depends upon…
the type of wave,
the composition of the medium, and
the state of the medium
the rate of change of distance with time by definition.
the product of frequency and wavelength for periodic waves.
Frequency and wavelength are inversely proportional.
frequency waves have
frequency waves have
The speed of a wave is sometimes known as its wave speed.
The SI unit of speed is the
meter per second
One-dimensional wave equation
sin (2π (
/λ) + ϕ)
angular frequency (temporal frequency),
ω = 2πƒ
wave number (spatial frequency),