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=v
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
level
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
RED SHIFT
Formulas still work for both types of red shift if v<c…read more

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