Physics Review Question

Unit: Waves
Year: 1996 Question#: 55
Question: An astronomer on earth studying light coming from a star notes that the observed light frequencies are lower than the actual emitted frequencies. The astronomer concludes that the distance between the star and the earth is

(1 ) decreasing
(2 ) increasing
(3 ) not changing


What is this question really asking?


Explanation by: Chad H

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Answer 1
decreasing

INCORRECT This answer is incorrect because the frequecy would be higher if the distance between the two were decreasing. return to top























Answer 2
increasing

CORRECT

This is correct because this relates to the doppler effect. Think about a train, when the train comes close to you the frequency increases and is higher, which also becomes louder. When the train is right in front of you, you hear the real sound of the train. When the train passes you, the noise is lower and the frequency decreases. In this problem the frequency is lower, therefor the distance between the two should be increasing if the frequency seen is lower.
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Answer 3
not changing

Incorrect

This is wrong because you would be stationary if it was not changing. Consult the doppler effect. return to top











































What's this question really asking?

The question wants to know if you are getting closer to an object or further away by noticing the light frequecies between the star and the earth. return to top

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