1. When hydrogen atoms are giving off energy in the form of light, they emit lig
ID: 1881764 • Letter: 1
Question
1. When hydrogen atoms are giving off energy in the form of light, they emit light specifically at wavelengths of 410.2 nm, 434.0 nm, 486.1 nm, and 656.3 nm. This is called the emission spectra of hydrogen.
In the 1920's, Edwin Hubble, while studying the stars of distant galaxies, found that for some, their emission spectra had peaks at 411.54 nm, 435.50 nm, 487.75 nm, and 658.47 nm. Hubble knew that these wavelengths did not correspond to any known element and that it was not likely that a combination of other elements or molecules was responsible. He did notice that these spectral lines corresponded to hydrogen's emission spectra except that they were all 0.0033 percent longer in wavelength than they should have been for a hydrogen spectra. Hubble deduced that this red-shift must be because of a Doppler effect. His calculations showed that these galaxies must be moving away from earth at 1 x 106 m/s (one million meters per second)!
a) If you were driving in a VERY fast car, how would the things you approach look different from normal? How would the things you drive away from look different? Explain.
b) Why do you think Hubble's discovery that the universe is expanding would have been impossible without instruments that could precisely measure emission spectra?
Explanation / Answer
(a) When you sitting in a car which is at very fast speed and you are approaching a source which emits light of different wavelengths.
Then Doppler's effect came into role and because of that we observed an decreased wavelengths.
(b) Because without measuring the emission spectra one cannot say that the universe is expanding or not. And to measure emission spectra it is very important to measure the emmision spectra precisely . If you are not able to measure it precisely a small difference in wavelength can change in velocity of expanding is large amount.
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