GRE0877 Q#55

Catria
Posts: 353
Joined: Fri Oct 26, 2012 4:14 pm

GRE0877 Q#55

Postby Catria » Thu Mar 06, 2014 9:02 pm

A distant galaxy isobserved to have its hydrogen-b line shifted to a wavelength of 580 nm, away from its laboratory wavelength of 434 nm. Which of the following gives the approximate velocity of recession of the distant galaxy? (Note: \frac{580}{434}=\frac{4}{3})

How could the recession speed be 0.28c?

TakeruK
Posts: 813
Joined: Mon Jan 02, 2012 3:05 pm

Re: GRE0877 Q#55

Postby TakeruK » Fri Mar 07, 2014 1:59 am

You have to apply the relativistic doppler effect (http://en.wikipedia.org/wiki/Relativist ... ler_effect)

\frac{\lambda_o}{\lambda_s} = \sqrt{\frac{1+\beta}{1-\beta}}

The fraction on the left is 4/3, as the question said. So you just have to solve for beta, and beta=0.28 works. (beta=v/c)

Catria
Posts: 353
Joined: Fri Oct 26, 2012 4:14 pm

Re: GRE0877 Q#55

Postby Catria » Fri Mar 07, 2014 6:06 pm

TakeruK wrote:You have to apply the relativistic doppler effect (http://en.wikipedia.org/wiki/Relativist ... ler_effect)

\frac{\lambda_o}{\lambda_s} = \sqrt{\frac{1+\beta}{1-\beta}}

The fraction on the left is 4/3, as the question said. So you just have to solve for beta, and beta=0.28 works. (beta=v/c)


Thank you... with 9677 and 0877 for practice materials I will continue studying for the April test.




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