Wavelength: distance between two consecutive peaks.

Frequency: number of seconds for a wave to pass a point.

Period: number of waves passing a point per second.

v = f λ

v: wave speed (m/s), f: frequency (Hz), λ: wavelength: m

Phase difference: how much a wave is in front of another.

Phase difference is measured in fractions of a wavelength, degrees or radians

In phase: 360^{o} or 2π radians. Anti-phase: 180^{o} or π radians

Transverse wave: vibrations are perpendicular to direction of wave e.g. EM

Longitudinal wave: vibrations are parallel to direction of wave e.g sound.

Polarisation: when oscillations only occur in one of the directions perpendicular to the direction of the wave.

Transverse waves can be polarised, longitudinal waves can't be.

To polarise waves, use a polariser or polarising filter.

If two polarisers have the same transmission axis, the intensity of the transmitted light is maximum.

If two polarises are perpendicular, no light will pass through.

Uses: polarised sunglasses (vertically polarises light to reduce glare), polaroid cameras (intensifies colour), radio signals.

Stationary wave: superposition of two waves with same frequency and wavelength and similar amplitude, in opposite directions.

Superposition: when two or more waves with the same frequency arrive at a point, the resultant displacement is the sum of the displacements of each wave.

Waves in superposition can undergo constructive or destructive interference (displacement gets smaller)

Constructive interference: path difference of nλ

Destructive interference: path difference of nλ/2

Path difference: the difference in distance travelled by two waves from their sources until they meet.

Harmonics: λ/2, λ, 3λ/2, 2λ etc. are where the stationary waves form from a string fixed at one end, and fixed to a driving oscillator at the other.

First harmonic equation:

f: frequency (Hz), l: length of string (m), T: tension (N), μ: mass per unit length

Coherent waves: when waves have a constant phase difference and same frequency.

w = λD/s

w: fringe spacing (m), D: distance to the screen (m), s: slit separation