Vibrations that transfer energy from one place to another without transferring the medium along with it.
Waves that need a medium are sound waves, seismic and water waves.
Waves that do not are electromagnetic radiation which can travel through a vacuum.
Transverse
Oscillations are at right angles (perpendicular) to the direction of the travel
Electromagnetic radiation are examples of this.
Water and Secondary seismic waves are also this.
Longitudinal
Oscillations are at the same direction as the direction of the energy transfer.
Sound waves, Primary seismic waves and water waves are this.
Compressions and rarefactions
Compressions are where particles move closer together
rarefactions are where particles move away
Amplitude
The distance from the highest or lowest point in waves to the undisturbed position.
Wave length
Length from one wave to another at the same point. Crest to crest/ trough to trough.
Measured in Metres (m)
Frequency
Number of waves produced per second. Also the number of waves that pass through a point a second.
Measured in Hertz (Hz)
v = f × λSpeed (m/s) = Frequency (Hz) * Wavelength (m)
Refraction
Sound waves and light rays change speed when they pass a boundary between two substances with different densities e.g. glass and air.This causes them to change direction.This doesn't happen for waves if they hit the boundary at 90 degrees. They will carry straight on without changing directions.
Diffraction
When waves meet a gap in a barrier and they spread out.
The spread is affected by how wide the gap is compared to the wavelength of the wave
Significant diffraction only happens if the gap size is around the same as the wavelength of the wave.
Reflection
When sound and light waves reflect from surfaces.
They obey the law of reflection
The angle of incidence is equals the angle of reflection
The normal is a line drawn perpendicular to the reflector
The angle of incidence is the angle from the normal to the light ray going to the reflector
The angle of reflection is the angle between the reflected ray to the normal.
Images appears from a point behind the mirror. They are virtual, upright, and laterally inverted.
Ray diagram
Sound
They can travel through solid liquids and gases.
Amplitude show how loud the sound is
the frequency shows what the pitch is.
A range of human hearing is 20 Hz to 20,000 Hz
Electromagnetic radiation
Light can be split up using a prism to form a spectrum of colours.
There are other types of electromagnetic radiation with different wavelengths
from lowest wave length to highest :
Radio waves used in TV signals and radios
Microwaves used in mobile phones and TVs
Infrared used in optical fibre communication
Light used in seeing
Ultraviolet used to detect forged bank notes
X rays used in medical images of bones
Gamma rays used to kill bacteria and cells.
Radio waves are able to diffract at gaps between hills so they can be received behind hills.
They don't need a repeater for people to receive the signals.
Microwaves do as they cannot diffract and requires a line of sight. Repeaters broadcast the signal again so it travels further.
Microwaves used for mobile communications are not harmful as they are too weak to damage tissues by heating and they are not ionising Microwaves can pass through the ionosphere so they can be used to communicate with satellites
Radio waves can also be reflected from the ionosphere which is an electrically charged layer in the upper atmosphere.
They can receive signals even when not in sight of the transmitter as the earth's surface curves.
Visible light lets us see, books, videos and light signals are examples of how we communicate with light. Visible light need transmitters and receivers to be in a line of sight.
Infrared can be used to heat up food but also used to communicate through optical fibres.
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