Waves (5) Flashcards
Wave motion
transfers energy and information without transferring matter.
Transverse waves
oscillations are perpendicular to the direction of energy transfer, e.g. EM waves.
Longitudinal waves
oscillations are parallel to the direction of energy transfer, e.g. sound waves.
Wavelength
the distance between equivalent points in successive cycles (wave peaks).
Amplitude
the maximum displacement from the undisturbed position (for a wave).
Refraction
is the change of wave speed and direction at a boundary when a wave travels from one medium to another.
Reflection
occurs when a wave bounces off a surface. The angle of reflection equals the angel of incidence.
Total internal reflection
of light is the complete reflection of light at a boundary within a material that has a higher refractive index than its surroundings.
Progressive wave
a wave that travels through a substance or a space, transferring energy.
Hertz
the unit of frequency, equivalent to s-1.
Period
the time for one complete cycle, measured in seconds.
In phase
particles that move in phase move in the same direction with the same speed. The particles have the same displacement from their mean position. Particles in phase are separated by a whole number, n, of wavelengths, nλ.
Out of phase
particles along a wave that move out of phase are at different points in their cycle at a particular time.
Antiphase
particles in a wave that move in antiphase move in opposite directions at the same speed. The particles have opposite displacements from their mean position. Particles moving in antiphase are separated by a distance of a whole number, n, of wavelengths plus an extra half wavelength, nλ+λ/2.
Phase difference
is measured as a fraction of the wave cycle between two points along a wave, separated by a distance x.
nλ+λ/2
Mechanical waves
cannot travel through a vacuum, but need a medium to travel through.
Polarisation
when the oscillations of the wave are confined to one plane, the wave is a polarised wave. For example, in an electromagnetic the electric field might be confined to just the vertical plane. These waves are said to be vertically polarised.
Crossing
if a second polarising filter is held at right angles to the original filter, this is called crossing the filters.
Angle of incidence, ϴ_i
is the angle between the incident ray and the normal.
Normal
an imaginary line at right angles to the boundary between two materials.
Angle of refraction, ϴ_r
is the angle between the refracted ray and the normal.
Refractive index
the ratio of a wave’s speed between two materials. It is normally quoted for light travelling from a vacuum into a material.
Critical angle
is the angle of refraction for which the angle of incidence is 90°.
Optical fibre
is a thin glass (or plastic) fibre that transmits light.
Step index optical fibre
is an optical fibre with a uniform refractive index in the core and a smaller uniform refractive index for the cladding.
Material dispersion
is the spreading of a signal caused by the variation of refractive index with wavelength.
Pulse broadening
occurs when the duration of a pulse increases as a result of dispersion in an optical fibre.
Modal dispersion
is the spreading of a signal caused by rays taking slightly different paths in the fibre.
Absorption
occurs when energy from a signal is absorbed by the optical fibre in which it travels.
