Electromagnetic Waves

     - consists of an electric field and a magnetic field
     - they are at rightangles to each other (perpendicular)
     - they are therefore transverse waves
     - unlike other waves there are no particlesvibrating just the field itself
     - therefore they can travel in a vacuum whereas other waves cannot

Production and transmission of E Waves

     - the source of these waves is the changein the fields caused by electrons changing speed or direction inside an
     atom
     - all E waves travel at 300,000 km / sec ( the speed of light) in a vacuum
     - they will travel at slower speeds when going through denser materials

Electromagnetic Spectrum

     - the different electomagnetic waves are arranged according to their wavelengths and frequency in a continuum
     called the electromagnetic spectrum
     - long wavelengths with low frequency on the left
     - short wavelengths with high frequencies on the right
     - the amount of energy that is carried depends on the frequency

          -high frequencies have high energy
          -low frequencies have low energy

     - only a small section of the continuum is vibrating at a level that humans can detect with our eyes ( the visible
     spectrum)
     - because the differences in the wavelengths, frequencies and energy are so great the spectrum is divided up into
     sections

Radio waves

     - lowest frequency andlongest wavelength
     - produced when charged particles move back and forth in an antenna
     - we can vary (modulate) either the size (amplitude) or the frequency of the waves
     - AM amplitude modulation or FM frquency modulation
     - sound portion of TVis AM and picture part is FM waves
     - radio waves can be interferred with (mountains , metal structures)
     - radio waves can be used in medicine to create pictures (MRI)
     - astronomy uses radio telescopes to "listen" in on space objects

Microwaves

     - a special type of radio wave
     - microwaves in oven pass through some things and absorbed by others
     - used in communication signals in cell phones etc.
     - RADAR - radio detecting and ranging use microwaves as well
     - send on waves and detect them as they bounce off an object
     - police use radar and the doppler effect to register speed

Infrared

     - waves with frequencies just below visible light frequencies
     - can be felt as heat
     - infrared cameras and goggles show images of the heat from an object
     - thermograms are special pictures showing hot and cold areas

Visible light

     - these frequencies can bedetected bythe receptors in our eyes
     - each colour has its own frequency
     - R ed O range Y ellow G reen B lue I ndigo V iolet
     - nearly half the energy from the sun is in this frequency range (spectrum)

Ultraviolet

     - just beyond the violet visible portion
     - these rays have a higher frequency and therefore can do more damage
     - used to kill germs in hospitals and to protect food in processing
     - some insects can "see" this range
     - these wavelengths are what cause sunburns and some cancers
     - the ozone layer in the atmosphere protects life onEarth from most of the ultraviolet rays from the sun, without it
     life as we knowit would die off

XRays

     - have enven more energy than ultraviolet so can pass through things
     - softer material allows them through
     - denser things (bone) do not
     - XRays are helpful but can also cause problems so lead aprons used to protect parts from exposure to the Xrays
     when possible
     - strong sources of this energy type are found in space

Gamma

     - these have the highest frequencies and therefore are the most dangerous
     - certain radioactive isotopes give off this energy type
     - because they have so much energy they can go through things that other energy forms cannot
     - they can be used in medicine (as dyes) to help detect diseases

Visible Light

     - objects that give off their own light are called luminous
     - objects that reflect light from somewhere else are called illuminated

Production of Light

     - 3 types of luminous objects are incandescent, fluorescent ,neon lights
     - incandescent
     - coil inside the light resist electricity, heat up, and glow
     - fluorescent
     - electricity causes gas in tubes to be excited producing ultraviolet light to cause the phophors coating to glow
     - less electricity needed and less enrgy lost as heat
     -neon
     - electricity causes gas to glow
     - depending on the gas in the tube, different colors produced

Waves or Particle

     - since the 1800's the idea of light as a wave answered all questions
     - in the 1900 though an experiment with light on different metals produced a current of electrons in only instances
     - the wave idea should produce electricity with all colours of light, but it might take longer with certain colours, this
       did not happen
     - the idea that light might be a stream of particles could explain the experiment
     - the idea of a photon (particle of light) was introduced
     - photons of different colours would have different amounts of energy and therefore cause different results
     -since photons and electrons (electricity) were involved they called it the photoelectric elffect
     - we use this effect for motion detectors and alarms etc.
     - scientists now describe light and other electromagnetic waves as both waves and particles