Waves Revision Notes

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  • Created on: 03-04-16 10:45
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Waves
Progressive wave (moving) carry energy &does not transfer material.
Wave caused by something making particles or fields oscillate at source. The oscillations pass
through medium as wave travels and carries energy. Wave transfers energy away from source so
source of wave loses energy.
We know waves carry energy because:
Electromagnetic waves cause things to heat up
Xrays and gamma knock e out of orbits causing ionisation
Loud sounds cause large oscillations of air
Wave power can be used to generate electricity
Reflection ­ wave bounced back when hits boundary
Refraction ­ Wave changes direction as enters different medium. Change in direction is result of
wave slowing down or speeding up
Diffraction ­ wave spreads out as passes through gap or round obstacle.

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Wave Speed
Distance travelled is WL
Time taken to travel 1 WL is period of wave which is equal to 1
f
Electromagnetic Wave Speed in a Vacuum
1
C = 3.…read more

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Measuring Wave Speed in Water
1) Record depth of tank with ruler
2) Use ripple tank dipper to create vibrations with regular freq. in tank
3) Dim main lights and turn on strobe light
4) Inc. freq. of strobe light from 0 until waves appear to be standing still, this is when
freq. strobe light is equal to freq. of water waves
5) Use ruler and white paper below tank to measure distance between several peaks and
dividing this by no. troughs in between.…read more

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Longitudinal ­ displacement of particles or fields is along direction of energy propagation.
Example: Sound.
Sound waves have alternate compressions and rarefactions of the medium it travels through.
Some type of earth quake shockwaves are also longitudinal (pwaves).
Polarised
Waves
Shaking rope by moving hand up and down or side to side or in mixture directions it makes
transverse waves but if try to pass rope through vertical fencing the wave will only get through if
vibrations are vertical.…read more

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Superposition of Waves and Formation of Stationary Waves
Stationary Waves ­ superposition of 2 progressive waves with same freq., WL or amplitude
moving in opposite directions. No energy transmitted.…read more

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At node, theres total destructive interferance
At antinode, theres constructive interference
First Harmonic ­ stationary wave vibrating at its lowest possible freq.
In figure 3.6 theres one loop with node at each end. ½ WL fits onto string so WL is double length of
string.
1
f=2l T
Second Harmonic
­ twice freq. of 1st .
2 loops with node at each end and middle, two ½ WL fit on string so WL = length of string.
Third Harmonic ­ 3x freq.…read more

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