Waves Flashcards
Wave speed
speed = frequency x wavelength c = fλ
Period
f = 1/T
First Harmonic
f = 1/2L x sqrt T/μ
Fringe spacing
w = λD/s
Diffraction grating
d sinθ = nλ
Law of refraction (snells law)
N₁ sinθ₁ = N₂ sinθ₂
Critical angle
sinθ꜀ = N₂/N₁ as long as N₁ > N₂
Define phase difference
How much a waves lags behind another wave
What is a progressive wave?
A wave that transfers energy from one place to another without transferring matter
What is the equation for phase difference in radians
2πd/λ
What is the phase difference between constructive waves
2π
What is the phase difference between destructive waves
π
What is a longitudinal wave?
A wave where oscillation of the particles is parallel to the direction of the wave
What is a transverse wave?
A wave where the oscillation of the particles is perpendicular to the direction of the wave
What is plane polarisation?
A method of allowing only transverse waves orientated in the same direction
What is a standing wave?
A wave that is the result of the superposition of two waves with the same amplitude, frequency and speed travelling in opposite directions
Define the principle of superposition
When two or more coherent waves meet, the total displacement at a point is the sum of displacements of each wave at that point. Waves superpose upon each other by interfering and either produce constructive or destructive interference
Define total internal reflection
When a ray of light reaches a boundary with a medium that ahs a lower refractive index and is completely reflected. The angle of incidence is greater than the critical angle
Define the term refractive index
The ratio of the velocity of light in a vacuum to its velocity in a medium
Define absorption (optical fibres)
Where part of the signals energy is absorbed by the fibre which reduces the amplitude of the signal
Define modal dispersion
Light rays enter the fibre at different angles and therefore take different paths. The rays take a different amount of time to travel through the fibre
Define pulse broadening
When the pulses of light spread out as thy travel which can cause two consecutive pulses to overlap
What two conditions are needed for total internal reflection?
The medium has to have a higher RI
The critical angle has to be exceeded
