1. 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.
Diffraction
When waves pass through a narrow gap they spread out. Polarisation
Most diffraction occurs when width of gap = wavelength Properties of waves A Polaroid filter can produce plane-
polarised waves where the vibrations are in
Important for satellite dishes
one plane only.
Sound is caused by
Waves and Optics
longitudinal vibrations of the If the angle of incidence is more
particles of air, liquid or than the critical angle then there
solid, in a backwards and is total internal reflection - used
Refractive index = speed of light in vacuum
forwards motion., causing Sound Speed of light in medium
in optical fibres.
compressions and Sin c = nr
rarefactions.
ni
n = sin i
A louder sound has larger
amplitude. sin r
Ultrasound Lenses
As the frequency increases so does the pitch of a note. Seismic waves Object beyond 2F Object between F and 2F
We can hear from 20Hz to 20kHz (the upper threshold of human
hearing). 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 F
frequencies and breaking up kidney stones. faster than the transverse S (shake) waves.
P waves can also go through the liquid core of
Pre-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.