Refraction, diffraction, interference Flashcards
How do you find the refractive index?
n = speed of light in vacuum / speed of light in substance
What is the critical angle?
The angle for which the angle of refraction is 90’ for light going from optically-dense materials to less optically dense materials.
When does light refract towards the normal?
Going from less to more optically dense
When does light refract away from the normal?
Going from more to less optically dense
What is TIR?
Total internal reflection, when light is moving from an optically dense to less optically dense material and the angle of incidence is more than the critical angle. So entirely reflects and stays in the 1st material.
List reasons for signal degradation in optical fibres
Absorption (every time it reflects, reducing amp), pulse broadening (pulse gets broader, reducing quality and causing overlaps), modal dispersion (different paths if the core is wide), material dispersion (white light will disperse over time, so use monochromatic)
What should you use to find out how far a wave has travelled?
Trig! For those silly interference questions
What happens in Young’s double slit experiment?
Waves split into 2 coherent beams, which superpose. Constructively when path diff is n, destructively when path diff is n + 1/2
What is the fringe separation equation?
w = lambda D / s. w is distance between 2 adjacent maxima/minima (from centres), lambda is wavelength, D is distance to screen, s is slit seperation.
List wavelengths of visible light, from lowest to highest
Blue, green, red
State what happens with single-slit diffraction for monochromatic light
Very bright central fringe, twice as wide as others. Outer fringes are all same width and decrease in brightness with distance.
State what happens with single-slit diffraction for white light
A bright white central maximum, then less bright fringes that are spectra, with blue on the inside and red on the outside.
Explain what happens with a diffraction grating
Monochromatic light produces sharp interference patterns. Central max is brightest and 0th order. 1st order is first on either side, n = 1. Etc etc.
What is the diffraction grating formula?
d sin (theta) = n lambda, d is slit separation and n is the order of the maximum.
What do coherent waves have?
The same frequency and a constant phase difference.
