Tuesday 7 April 2009

The Doppler Effect, Red Shift, Blue Shift and Frequency For all most a century people have been witnessing something very strange. Ever since the Industrial revolution transport started, i.e. trains, and as soon as an object become fast enough it produced a noise, they noticed that the further away the object is the quieter the sound is, but the closer the noise the louder the sound but as soon as it moves away from us it suddenly becomes quiet again. This interested an Austrian physicist called Christen Doppler who proposed this in 1842 and named it after him, "The Doppler Effect" What he said confirmed that the sound's pitch was higher than the emitted frequency when the sound source approached him, and lower than the emitted frequency when the sound source was further away from him. (Notice on the diagram how the wavelength (period) is shorter than the low frequency wavelength this shows that the high frequency graph has a higher pitch than the low frequency graph) this graph can show you what it would look like if a car drove past you, the high frequency graph would be when the car is closer to you when the low frequency graph would be when the car is further away from you. This also can lead us to new topic which is Red Shift, Blue Shift and Frequency but both are very similar. I have mentioned some bits about frequency but there are very important bits that I have missed out which might make the Doppler Effect make more sense. Frequency has a spectrum but with most things there is a problem and in this topic there is no exceptions, the problem is light and sound. Lets take a car as an example, the car emits light and sound these are represented by circles. This shows that the car is stationary, but look at the circles when the car is moving to the right, but when an object is moving to the right there is less space between the lines than the left. This causes a frequency change, as the lines on the right are closer together causing a higher frequency when the lines on the left are further apart causing a lower frequency. If we look at the frequency spectrum on the right the colour is mainly red, we call this Red Shift, and if we look at the frequency spectrum on the right the colours are mainly blue, we call this Blue Shift. So as you can see it all adds together in just one article. Hope this has helped. By Cameron Webb