# P1.5 The Use Of Waves For Communication

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GCSE Physics (P1) Mind Map on P1.5 The Use Of Waves For Communication, created by killthemoment on 08/09/2014.

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P1.5 The Use Of Waves For Communication
1 P1.5.1 General Properties Of Waves
1.1 Waves transfer energy and may be either transverse or longitudinal. In a transverse wave the oscillations are perpendicular to the direction of energy transfer. In a longitudinal wave the oscillations are parallel to the direction of energy transfer.
1.1.1 Electromagnetic waves are transverse, sound waves are longitudinal and mechanical waves may be either transverse or longitudinal. All types of electromagnetic waves travel at the same speed through a vacuum (space). Electromagnetic waves form a continuous spectrum.
1.1.1.1 As waves travel, they set up patterns of disturbance. The amplitude of a wave is its maximum disturbance from its undisturbed position. The wavelength of a wave is the distance between a point on one wave and the same point on the next wave. The frequency of a wave is the number of waves produced by a source each second. It is also the number of waves that pass a certain point each second.
1.1.1.1.1 The speed of a wave is related to its frequency and wavelength, according to this equation: v = f × λ where v is the wave speed in metres per second, m/s, f is the frequency in hertz, Hz and λ (lambda) is the wavelength in metres, m.
1.1.1.1.1.1 Longitudinal waves show areas of compression and rarefaction.
1.1.1.1.1.1.1 Waves can be reflected, refracted and diffracted. Significant diffraction only occurs when the wavelength of the wave is of the same order of magnitude as the size of the gap or obstacle. Waves undergo a change of direction when they are refracted at an interface.
1.1.1.1.1.1.1.1 Radio waves, microwaves, infrared and visible light can be used for communication.These waves are typically used as: radio waves – television, and radio (including diffraction effects); microwaves – mobile phones and satellite television; infrared – remote controls; visible light – photography.
2 P1.5.2 Reflection
2.1 The normal is a construction line perpendicular to the reflecting surface at the point of incidence. The angle of incidence is equal to the angle of reflection. The image produced in a plane mirror is virtual.
3 P1.5.3 Sound
3.1 Sound waves are longitudinal waves and cause vibrations in a medium, which are detected as sound. The pitch of a sound is determined by its frequency and loudness by its amplitude. Echoes are reflections of sounds.
4 P1.5.4 Red-shift
4.1 If a wave source is moving relative to an observer there will be a change in the observed wavelength and frequency. This is known as the Doppler effect. The wave source could be light, sound or microwaves. When the source moves away from the observer, the observed wavelength increases and the frequency decreases. When the source moves towards the observer, the observed wavelength decreases and the frequency increases.
4.1.1 There is an observed increase in the wavelength of light from most distant galaxies. The further away the galaxies are, the faster they are moving, and the bigger the observed increase in wavelength. This effect is called red-shift. The observed red-shift provides evidence that the universe is expanding and supports the 'Big Bang' theory (that the universe began from a very small initial point).
4.1.1.1 Cosmic microwave background radiation (CMBR) is a form of electromagnetic radiation filling the universe. It comes from radiation that was present shortly after the beginning of the universe. The 'Big Bang' theory is currently the only theory that can explain the existence of CMBR.

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