8Light wavesLight slows down as it goes from air to glass/water
9Snell’s lawThere is a relationship between the speed of the wave in the two media and the angles of incidence and refractionRay, NOT wavefrontsir
10Snell’s lawspeed in substance 1 sinθ1speed in substance 2 sinθ2=
11Snell’s lawIn the case of light only, we usually define a quantity called the index of refraction for a given medium asn = c = sinθ1/sinθ2cmwhere c is the speed oflight in a vacuum and cmis the speed of light in themediumcvacuumcm
12Snell’s lawThus for two different mediasinθ1/sinθ2 = c1/c2 = n2/n1
13Refraction – a few notes The wavelength changes, the speed changes, but the frequency stays the same
14Refraction – a few notes When the wave enters at 90°, no change of direction takes place.
16irAsk them to set up the experiment as above. Gradually increase the angle of incidence. What happens?
17Data collection and processing Table of raw results with quantity, unit, uncertainty and an agreement between the uncertainty and precision of measurementsData correctly processed (including graphs and line of best fitUncertainties correctly propagated (calculated) and error bars on graph (max/min line of best fit)
18Conclusion and evaluation Compare result with actual result (referenced)Discussion of possible systemmatic errorsIdentification of weaknesses with relevant significanceImprovements based on weaknessesNo “waffly” terms!
33INTERFERENCE1. Constructive Interference - when the crests (or troughs) of two waves coincide, they combine to create an amplified wave.All waves can be ReflectedThe two waves are in phase with each other – there is zero phase difference between them.33
35INTERFERENCE2. Destructive Interference - where the crests of one wave are aligned with the troughs of another, they cancel each other out.All waves can be ReflectedThe waves are out of phase (or in antiphase) with each other – they are half a cycle different from each other.35
37Standing waves store energy, whereas travelling waves transfer energy from 1 point to another The amplitude of standing waves varies from 0 at the nodes to a max at the antinodes, but the same amplitude for all the oscillations along the progressive wave is constant.The oscillations are all in phase between nodes, but the phase varies continuously along a travelling wave.