Recent technological developments have allowed for greater use
of the electromagnetic spectrum
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Class Quiz on Focuses1 and 2 Objectives 1 20 Monday 1/3/09
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Electromagnetic Waves
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The full range of wavelengths of all electromagnetic waves. We
have made arbitrary divisions in the spectrum to divide these waves
into families or bands. Examples include; radio waves, light waves,
ultraviolet waves, X-rays. In reality the spectrum is a
continuum.
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Do not require a medium for propagation so can travel through
the vacuum of space. Travel at the speed of light in a vacuum. c =
3 x 10 8 ms -1, 300 million ms -1 EM waves are transverse waves
they consist of an oscillating magnetic and electric field that are
perpendicular to each other. http://www.phys.hawaii.edu/~teb/jav
a/ntnujava/emWave/emWave.html http://www.phys.hawaii.edu/~teb/jav
a/ntnujava/emWave/emWave.html
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Self propagating the oscillating electric field induces a
magnetic field and the oscillating magnetic field produces an
electric field... and so on... Can be produced by oscillating
electric charges. The waves produced have the same frequency as the
oscillating particles. The waves can be detected as they produce
electrical responses in the medium that they pass through.
http://phet.colorado.edu/simulations/si
ms.php?sim=Radio_Waves_and_Electro magnetic_Fields
http://phet.colorado.edu/simulations/si
ms.php?sim=Radio_Waves_and_Electro magnetic_Fields
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Compare sound waves and electromagnetic waves. Compare: Show
how things are similar or different
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Wave type SoundElectromagnetic Similarities Differences
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Complete the worksheet The Electromagnetic Spectrum and
Detecting the Bands. Identify the wave bands used in
communication.
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Attenuation of EM waves refers to the reduction in amplitude or
intensity of EM waves as it passes through a medium. We experience
this in our everyday lives in a number of ways. Our mobile phone
signal strengths decrease the further we are from the phone tower.
As you travel away from Sydney the signal from Sydney based radio
stations gradually decrease until you can no longer receive the
station. The further the distance we are from a source of light the
lower the intensity of the light appears to be
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In order to be able to work out the mathematical relationship
between the variables we need to obtain a straight line so that we
can use y = mx + b. These results suggest that the relationship
between Intensity and distance may be a y = 1/x type relationship.
Next step is to graph Intensity vs 1/d and see what shape our graph
is.
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Select two points on the line of best fit (do not use data
points!). Select points that are well apart and easy to read on the
graph. Draw a gradient triangle and use rise over run.
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From the prac we determined that Intensity (I) and distance (d)
from the source were related by an inverse square relationship.
Where I = Intensity (lux) d = distance from the source (m) This is
known as the Inverse Square Law. We will see many other examples of
Inverse square relationships throughout this course.
