Waves definitions Flashcards
Longitudinal Wave
A wave in which the particles move back and forth in the direction of wave
travel, e.g. sound waves.
Transverse Wave
A wave in which the particles move perpendicular to the direction of wave
travel e.g. water waves.
Crest
The top point (peak) of a wave.
Trough
The bottom point of a wave.
Amplitude
The vertical distance from the axis to the top of the wave (crest) or bottom of
the wave (trough). It is also half the vertical height of the wave.
Wavelength
The horizontal distance from one crest to the next crest, one trough to the next
trough or one point on a wave to the same point on the next wave.
Travelling Wave
A transverse wave that can be represented mathematically with an equation.
Phase Difference
A measure of how much one wave lags behind another, or one point lags
behind another on the same wave.
Stationary (Standing)
Wave
Formed by the constructive interference of two waves, of the same frequency
and amplitude, travelling in opposite directions.
Node
A point on a stationary wave where the amplitude is zero.
Antinode
A point on a stationary wave where the amplitude is a maximum.
Interference
Occurs when coherent waves overlap.
Coherence
When waves have a constant phase difference between them.
The waves will also have the same frequency, wavelength and speed.
Phase
Used to describe how ‘in tune’ two waves are when overlapping.
Constructive
Interference
When two waves of equal amplitude meet in phase, they combine to form a
wave of twice the amplitude.
Destructive
Interference
When two waves of equal amplitude meet out of phase, they combine to form
a wave of zero amplitude.
Path Difference
The difference in distance travelled by waves from different coherent sources.
Maximum/Maxima
A point/points of constructive interference.
Minimum/Minima
A point/points of destructive interference.
Order Number (m)
An integer (whole number) value which describes the point on the interference
pattern (screen) you are dealing with.
Division of Amplitude
Interference of light produced by thin (oil) films, coated camera lenses and thin wedge interference.
Division of Wavefront
Interference of light produced by Young’s double slit experiment.
Geometric Path Length
The distance travelled by a wave through a material, not taking into account the refractive index of the material.
Optical Path Length
The distance travelled by a wave through a material, taking into account the
refractive index of the material.
Optical Path Difference
The difference in optical path lengths.
Blooming of Lenses
Placing a special thin coating such as magnesium fluoride on camera or
binocular lenses to ensure that maximum light is transmitted through the lens.
Fringes
The successive pattern of bright and dark bands in an interference pattern.
Fringe Spacing (Δx)
The distance between adjacent fringes of the same type (i.e. bright or dark) in
an interference pattern.
Polarisation
An effect most commonly observed when using polarising lenses in sunglasses
which reduces the glare from reflective surfaces such as water or glass.
Light is said to be linearly plane polarised when the electric field oscillations
occur in only one plane.
Polariser
Allows light to pass through in one plane only.
Analyser
Often used together with a polariser. It is simply a second polariser.
If placed in front of a polariser and rotated to 90 ̊ , it will block the light
completely.
Brewster’s Angle
The angle of incidence which causes the reflected light to be fully plane-
polarised.
This occurs when there is an angle of 90 ̊ between the reflected and refracted
rays.
Absolute Refractive
Index
A number greater than or equal to 1 which indicates a material’s ability to
refract light.
It is also the ratio of the speed of light in a vacuum to the speed of light in the
medium.
