Radio Microwaves Infra-red (IR) Visible Ultra-violet X-ray Gamma Long wave 500m radio Are absorbed by water Heat is emitted by all hot In a laser all Absorbed by Absorbed by Come from the waves are reflected in food but pass through objects including ourselves. the waves are ozone, bone not nucleus. from the ionosphere. the atmosphere to Shiny surfaces reflect IR in phase – used sunblock and tissue Absorbed by AM waves have their satellites. but dark surfaces absorb IR. to read CDs. the skin. Electrons hit a lead. amplitude modulated by the sound. all travel at c, The Electromagnetic Spectrum wavespeed = frequency x wavelength through a vacuum as a Interference transverse When waves cross over, if two crests arrive in phase, we have constructive wave. interference. The path difference must be an even number of half wavelengths. But when a crest meets a trough we have destructive interference. DiffractionWhen waves pass through a narrow gap they spread out. PolarisationMost diffraction occurs when width of gap = wavelength Properties of waves A Polaroid filter can produce plane- polarised waves where the vibrations are inImportant for satellite dishes one plane only.Sound is caused by Waves and Opticslongitudinal vibrations of the If the angle of incidence is moreparticles of air, liquid or than the critical angle then theresolid, in a backwards and is total internal reflection - used Refractive index = speed of light in vacuumforwards motion., causing Sound Speed of light in medium in optical fibres.compressions and Sin c = nrrarefactions. ni n = sin iA louder sound has largeramplitude. sin r Ultrasound LensesAs the frequency increases so does the pitch of a note. Seismic waves Object beyond 2F Object between F and 2FWe can hear from 20Hz to 20kHz (the upper threshold of humanhearing). Frequencies above 20kHz are ultrasound.Used for industrial cleaning where dirt is broken up by the high The longitudinal P (push pull) waves travel Object inside Ffrequencies and breaking up kidney stones. faster than the transverse S (shake) waves. P waves can also go through the liquid core ofPre-natal scanning – the waves are reflected from the fetus. – no the Earth, unlike the S waves.damage to the fetus and shows up soft tissue.