Optics Flashcards
What is the refractive index of a substance?
n = c in vacuum / c in substance
Give the refractive index of air
approx 1
What is an optically dense substance?
a substance with a high refractive index, where light travels more slowly
State Snell’s law
n1sinθ1 = n2sinθ2
Which directions do rays of light bend when they enter a more optically dense substance?
towards the normal (to the surface)
What is the critical angle in total internal reflection
the angle at which the angle of refraction is 90deg
What is the purpose of the cladding of an optical fibre
allows total internal reflection to take place, protect the core from damage, prevents light from leaking out
Give two ways in which signal degradation can occur in fibres
absorption, pulse broadening
What is the consequence of pulse broadening in an optical fibre
Reduces the quality of the signal, can lead to a loss of data if pulses overlap
Define coherent waves
Waves with the same frequency and a constant phase difference
What is an interference pattern?
when waves with a constant phase difference superpose to produce cancellations and reinforcement at fixed positions
What is the path difference between two waves if they constructively interfere at a point?
a multiple of the wavelength, nλ
What is the fringe separation in a fringe pattern?
distance between the centres of 2 adjacent minima or maxima
Why are the fringes produced by red light farther apart than those produced by blue light in a double slit experiment?
as red has a longer wavelength
State the diffraction grating formula
dsinθ = nλ
