Recent technological developments have allowed for greater use of the electromagnetic spectrum

Class Quiz on Focuses1 and 2 Objectives 1 – 20 Monday 1/3/09

Electromagnetic Waves

 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.

 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.  a/ntnujava/emWave/emWave.html a/ntnujava/emWave/emWave.html

 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.  ms.php?sim=Radio_Waves_and_Electro magnetic_Fields ms.php?sim=Radio_Waves_and_Electro magnetic_Fields

 Compare sound waves and electromagnetic waves. Compare: Show how things are similar or different

Wave type SoundElectromagnetic Similarities Differences

 Complete the worksheet “The Electromagnetic Spectrum” and “Detecting the Bands”.  Identify the wave bands used in communication.

 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

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.

 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.

 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.