Doppler Effect and Red Shift revision notes

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  • Created on: 30-04-13 17:09
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Doppler Effect and Red Shift
The Doppler Effect
Doppler effect: the change in wavelength and frequency
Happens with all waves, including EM radiation
Siren: moves towards you- higher pitched then when moving away
The frequency and wavelength change because waves bunch together in front of the source
and stretch out behind it. The amount of bunching/stretching depends on velocity of source
Red Shift
Light source moves away: wavelength longer and low frequency = shifts light we receive
towards red end of EM spectrum = RED SHIFT
Red shift of light is emitted by a star moving away from us
BLUE SHIFT of light is emitted by star moving towards us
Amount of red/blue shift depends on how fast the star is moving
Higher velocity = more the waves are shifted
c if vc
Z= amount of red shift
v= recessional velocity (velocity that object is moving away from us at)
If v>0, red shift is positive
If v<0, red shift is negative ­ radiation is blue shifted
Increase in wavelength = red shift ALWAYS
Decrease in wavelength = blue shift
Observing red shift
Radiation spectrum of a moving source will be shifted depending on motion
Different atoms only absorb particular wavelength of light to excite photons to next energy
Work out red shift by looking at wavelength/ frequency of known absorption lines and
comparing them to what they should be

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If star is red shifted, f>(change)f, so (difference)f and z will be positive
z =- ww
W= wavelength
Cosmological red shift
All distant galaxies show red shift, moving away
Astronomers say space is expanding and light waves are being stretched = COSMOLOGICAL
Formulas still work for both types of red shift if v<c…read more


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