Waves

Waves

1. features of waves

   • All waves are a series of oscillations that transfer energy from one place to another.
   • Displacement- is the size of the oscillation at a particular time and place.
   • Wavelength- is the distance between two identical points on adjacent waves.
   • Amplitude- is the maximum displacement caused by the wave.
   • Speed- is how fast the disturbance moves, measured in metres per second.
   • period- is the time taken for one whole cycle of the wave to complete.
   • Frequency- is the number of waves that pass in each second. Measured in Hz

2. Measuring wavelength or period

   • Simplest method- measure the time for one period. A period is the top of one peak to the next.
   • Better method- measure the time for as many periods as possible, and divide by how many you measured.

3. Different waves-

   • Longitudinal- shows oscillations parallel to the direction of motion of the wave. If the wave was moving from right to left, the oscillations would also be right to left.
   • Transverse- shows oscillations at right angles to the direction of motion of the wave. If the oscillation was up and down, the wave could be movinf left to right.
   • Sine wave- normal wave. Square wave- squares
   • Standing wave- each particle oscillates with a different amplitude. At a node, amplitude is zero. At an antinode, amplitude is maximum.Every point is in phase- all of the particles in one part of the standing wave move up or down at exactly the same time.
     • Nodes- where there is no oscillation Antinodes- where the oscillation is greatest.
   • Travelling wave- as this wave passes by, every particle oscillates with the full amplitude of the wave. Every point in a travelling wave has a different phase- at any point in time, some points are moving up, and some are moving down.

4. Polarisation

   • Transverse waves can be polarised. A polarised wave has oscillations in one direction only.
   • Electromagnetic waves- EM waves are made up of electric and magnetic fields. They are at right angles to each other. The direction of the eletric field tells us the polarisation. If the electric field was vertical, then we call this vertically polarised.
   • Light- happens naturally when it reflects from a shint surface, such as wate. The 'glare' caused by the sun reflecting from still water is horizontally polarised light.
     • Sunglasses- sometimes contain polariod, this only lets through one polarisation of light.
   • Radio waves- polarisation depends on the aerial that produces the wave.
     • Horizontal bars- makes horizontally polarised radio waves. due to the electrons in the bars oscillate horizontally and make a horizontal electric field.
     • Vertical bars- makes vertically polarised radio waves. due to the electrons in the bars oscillate vertically and make a vertical electric field.
     • If it is to pick up the signal, the receiving aerial must match the polarisation of the transmitting aerial.

5. Electromagnetic waves

   • consist of an oscillating electric field with an oscillating magnetic field at right angles.
   • they can travel through a vacuum. They can also penetrate various substances. They will always be absorbed or scattered to a certain extent, reducing the amplitude of the waves.
   • 4 main sources
     • oscillating charges- charged particles, usually electrons, oscillate rapidly inside a transmitter. If the electrons oscillate up-down, vertically polarised waves are generated. A receiver that is vertical will allow electrons to pick up these waves. example of how a tv and radio transmitters work.
     • Electrons changing energy states inside atoms and molecule. if an electron loses energy inside an atom it is emitted as electromagnetic radiation.
     • Excited states of atomic nuclei- unstable nuclei of atoms shed excess energy as electromagnetic radiation.
     • Hot bodies- any object will emit a certain amount of electromagnetic radiation related to its temperature.

6. Wave equation: Speed= frequency/ wavelength

7. Electromagnetic spectrum

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