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What speed should a galaxy move with res...

What speed should a galaxy move with respect to us so that the sodium line at 589.0 nm is observed at 589.6 nm ?

Text Solution

Verified by Experts

Here `Deltalamda=lamda.-lamda=589.-589=0.66nm`
`impliesDeltalamdagt0`
`implies` Wavelength increases (or frequency decreases)
`implies` Corresponding spectral line will be obtained towards red end of spectrum. Such phenomenon is called "Red Shift", which shows that galaxy is moving away from us.
For red shift, radial outward velocity of galaxy (or velocity of galaxy away from us) is given by formula,
`v=c((Deltalamda)/(lamda))`
`=3xx10^(8)((0.6xx10^(-9))/(589xx10^(-9)))`
`=0.003056xx10^(8)`
`:.v=3.056xx10^(5)m//s`
Note: When source of light moves towards us, we obtain "Blue Shift", due to decrease in wavelength (or increase in frequency). At this time, velocity of source of light towards us is given by formula,
`v=-c((Deltalamda)/(lamda))`
(Where `Deltalamda=lamda.-lamdalt0` because `lamda.ltlamda`)
What speed should a galaxy move with respect to us so that the sodium line at 600 nm is observed at 605.0 nm?
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