Require a medium for transmission->no travel in a vaccume
Source vibrates->causes vibrations
Energy from vibrations->through medium(transmitted by particles within medium)
Transverse - Oscillations perpendicular to waves direction e.g water
Longitudinal - Oscillations parallel to waves direction e.g sound, within longitudinal waves are Compressions->compact sections, Refractions->spread out sections
Repetative motion about a fixed point
At REST=at the extreme of motion(most compact or most streached)
At MAXSPEED=either midpoint of the oscillation
Oscillaions have 3 properties:
2.T the period(time of oscillation)
Displacement-time graphs->Oscillating particles
1.Attach a pen to whats oscillating-> draws on card moving horizontally
2.Use a transmitter and reciever
Waveform=shape of graph
Phase=position in cycle -> 1(t=0), 1/4(t=T/4), 1/2(t=T/2), 3/4(t=3T/4), 1(t=T=1) ->1=1/2 but half is in antiphase like 3/4(moving in opposite direction to 1.
In a displacement distance graph it shows the position of all particles in a section of a wave in one instant(not one particles motion within the wave(displacement-time graph)).
Not all particles are in phase -> particles next to each other are at opposite positions.
Diagrams of longitudinal waves are very hard to draw this way. You can draw them as arrows in opposite directions, positive and negative displacements, (positive -> forward->like a peak) (negative<-backwards<-like a trough
Charged particles accelerated to cause electromagnetic waves.
Example - Radio waves -> electrons in ariel oscillate, this makes varrying electric and magnetic fields. Frequency=frequency of oscillation.
- variations in same plane as antenna(horizontal)
- variations at right angles to electric field oscillation(vertical)
Niether wave can exist without he other.
No medium needed.
To detect pass over charged particles, the particles pick up some of the energy and vibrate at the same frequency as the origional wave.
Can also occur due to 'quantum jumps' of electrons in atoms or from 'excited' nuclei -> these emit photons -> -packets of waves, -only a few nano seconds in duration -energy controls wavelength.
The speed of waves are different rates under different conditions:
Sound - 343ms^-1 @ 20 (c) in air,
331ms^-1 @ 0(c),
1497ms^-1 @ 25(c) in water
Light - 2.99792458x10^8 s^-1 in a vaccume,
2.99880297x10^8 ms^-1 in air
Determening speed of light in different mediums
Precision- small incremants in measue
Accuraccy-how close to true value
SIN i/ SIN r= a constant
When a wav changes medium the speed changes this changes the distance it travels per wave so changes the waves direction. The only exception is if the beam is traveling on the normal line.
Wavelength=speed x time
oMg=Vo/Vg=speed of wave in first medium/ speed of wave in second medium
Refractive index: ratio of wave speed between two mediums
A polarising filter blocks out oscillations, in all planes except one. If you use two at right angles to each other no waves can pass through.
Plane polarised = a transverse wave which only oscillates in one plane.
Reflected light is partially polarised.