# Cyberphysics - Waves Revision

## Terms

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What does a wave do?
A wave transports energy from one place to another
What are mechanical waves?
Mechanical waves use particles to transfer energy (neighbouring particles bump into each other and set their neighbours moving).

Eg. sound waves use air particles so it cannot travel through a vacuum (a vacuum is empty space with no particles in it at all!). Sound travels faster through solids than liquids than gases because the particles are more closely packed.
What are electromagnetic waves?
Electromagnetic waves don't use particle vibration to transfer their energy (in fact particles interrupt their progress through a material) and can therefore travel through a vacuum. e.g. light
What is the unit of frequency?
Frequency is measured in hertz (Hz)
What is the wave equation?
wavespeed = frequency x wavelength
Define a longitudinal wave.
The vibrations in a longitudinal wave are parallel to the direction in which the energy is travelling. Eg. sound.
Define a transverse wave.
The vibrations in a transverse wave are perpendicular (at right angles) to the direction in which the energy is travelling. Eg. light.
Define wavelength.
Wavelength (lamda a Greek letter 'l') is the shortest distance between two particles that are oscillating in phase. (Distance between two crests on a displacement/distance graph). It is measured in metres (m)
What is the period of a wave?
Period (T) is the time taken for one complete oscillation of a particle in the wave. (Distance between two crests on a displacement/time graph). It is measured in seconds (s).
What is amplitude?
Amplitude (A) is the maximum displacement from the mean position. (To the top of a crest or bottom of a trough from the middle line in either graph).
What is frequency?
Frequency (f) is the number of oscillations per second. It cannot be read directly off a graph. You need to find (T) from the displacement/time graph and then find its reciprocal (f =1/T)
What are analogue signals?
Analogue signals contain all the information as a continuously varying wave
What are digital signals?
Digital signals are a series of pulses - either high or low - on or off - sometimes expressed as binary code 1s and 0s.

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