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Physics Waves 2
Physics Spring Y12
| Question | Answer |
|---|---|
| Displacement definition | Distance of a point on a wave from its equilibrium position |
| Amplitude definition | The maximum displacement |
| Interference | Occurs when 2 waves in same place at same time. Displacement of the resultant wave equal to vector sum of the displacements of the individual waves at any point |
| Constructive interference | Occurs when 2+ waves are in phase (call it complete constructive interference when relevent) |
| Destructive interference | When in antiphase |
| Coherent waves | Waves with a CONSTANT PHASE DIFFERENCE (exact wording) |
| Double slit experiment what do the variables stand for | a = slit separation D = slit-screen distance x = fringe separation |
| Double slit experiment diagram | Path difference triangle is similar to triangle between midpoint of light waves and central max. Line perpendicular to make isocoles of light waves. Path difference is the small bit left over. |
| Double slit experiment proof | theta is angle between light wave midpoint and central max. Because similar, is also opposite path difference. tan = x/D sin = lambda/a for small angles: sin = tan |
| 'First fringe' | Not the central maximum |
| Path difference | Describes difference in oscillation pattern, given in terms of lambda. For constructive, path difference is n(lambda) Destructive, (n+0.5)lambda |
| Brightness proportionality to intensity | Directly proportional |
| Path difference and amplitude | Completely separate concepts - doesnt affect position of fringes just their brightness |
| Superposing waves | When 2 progressive waves of the same frequency are travelling in opposite directions in the same medium, they superpose. This creates a standing wave |
| Standing waves | No net energy transfer. All the points in each loop of a stationary wave are in phase (all at max/min, equi at once) but antiphase with adjacent loops The amplitude (MAX displacement) of adjacent points of the wave are different |
| Antinodes | Positions of max displacement |
| Nodes | Positions of zero displacement |
| Progressive waves definition | Transfer energy from one point to another without transferring the medium |
| Diffraction most obvious when | Gap roughly = wavelength |
| Harmonics on a string | We have to have a node at either end |
| Harmonics in a pipe with 2 open ends | Antinodes at either end |
| Harmonics | First one is called the fundamental frequency/first harmonic. Wavelength = 2L. frequency = f subscript 1 Second harmonic is just 2L/2 and 2F1 Etc |
| Harmonics in pipe with one closed end | Longitudinal wave so air molecules cant oscillate because of wall: must be a node standing still. Has to be a node at the closed end and an antinode at the open end (no limit on particles' movement) |
| Wavelengths in closed pipe harmonics | Fundamental: lambda subscript 1 = 4L, f1 Second harmonic - 4/3L Third - 4/5L |
| Types of harmonics that fit into closed pipe | Even multiples of quarter wavelengths dont fit in closed pipe (need to end on different of node/antinode) but we ignore that and just call the 2nd harmonic anyway. |
| Frequencies in closed pipe harmonics | V is constant, so f1 = V/4L f2 = 3V/4L |
| How to find speed of sound from closed pipe experiment | f = v/lambda This means a graph of f on y axis and 1/lambda on x axis Sound doesnt go through the water for harmonics, and there is a node at the closed end every half wavelength, so by listening for loud points we can estimate 1/2 wavelength |
| Waves out of phase on diagram how much path difference | Not necessarily 1/2 lambda - might not be in antiphase |
| How to ensure coherent waves emitted | Connect to same signal generator to ensure same polarity in waves |
| What happens if mic further from slits in double slit experiment | Lower amplitude at all points and high/low sections more spaced |
| In double slit experiment why might the laser go through a single slit first? | To diffract the laser light - ensures 2 coherent sources from double slit |
| An incredibly important piece of equipment for gave frequency changing, similar in terms of necessity to stuff like ammeters for electricity | SIGNAL GENERATOR |
| How does closed tube harmonics work | Pressure difference at open end so wave reflected so interferes to form standing wave |
| If setting up an experiment and Q says slit separation is 'about' 0.5mm | You have to mention properly measuring it |
| Metre rule | Show mms |
| How to improve accuracy of fringe separation | Increase D increases x, making measurements more accurate |
| If it gives you 2 metre rules and you have to assume measurements | Assume D is between 1 and 2m for working out x |
| How to describe movement of point on stationary wave | Oscillates continuously about equilibrium position/perpendicularly to central line (say it goes up and down ffs) |
| Because of everything in phase/antiphase on standing wave | Don't use phase difference numbers for stationary, really |
| Laser emitting uniform beam. What 2 quantities are needed to calculate intensity? | Cross-sectional area (LASER BEAM) and power Amplitude useless |
Created by:
Pyrogearos2