Doppler effect and red shift Flashcards
Doppler effect
when a wave source is moving relative to an observer, there is a change in the observed frequency and wavelength of the waves
sound waves in front of a moving car are compressed, resulting in a higher pitch, while sound waves behind are stretched, creating a lower pitch
red shift and the Doppler effect
the Doppler effect occurs for light waves and sound waves
a light source moving away from an observer will have a greater wavelength and a lower frequency, it is ‘red shifted’
a light source moving towards an observer will have a smaller wavelength and a higher frequency, it is ‘blue shifted’
discovery of red shift
1929
Edwin Hubble
discovered light reaching Earth from galaxies was red shifted
looked at the spectral lines in the absorption spectra of stars moving away from us
Explain how red shift suggests that the Universe is expanding [4]
the light received on Earth from most galaxies is red shifted
most galaxies are moving away from us
the furthest galaxies from us have the greatest red shift, so are moving away from us faster
this suggests that the Universe is expanding
Describe an example of the Doppler effect for:
a) sound waves [2]
b) light waves [2]
a) siren changing its frequency as it moves relative to the observer, frequency greater on approach to observer and lower on recession from observer
b) red-shift of light waves/spectral lines for light from a galaxy or star that is moving away from us
Suggest how the speed of a galaxy can be determined from the absorption lines in its spectrum [3]
absorption lines in the spectra of the light from the galaxy can be compared with the corresponding absorption lines of a stationary source
the difference in the position/wavelength/frequency can be used to calculate the speed of the galaxy
