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Firefox File Edit View History Bookmarks Tools Window Help 29 HW Mastering Physics: CH OR10 ion masteringphysics.com/myct/itemviewnoffset-next&assignmentP; 74057225 Firefox has prevented the outdated plugin "Adobe Flash from running on https://session.masteringphysics.com. 2017 Spring PHYS 2710 CH2h HW Alternate Exercise 29.82 Alternate Exercise 29.82 Part A A star in our galay is 4500 light-years from Earth, What's the distance to the quasar? yet it appears from Earth to be the same brightness as a distant quasar whose power output is 43 billion times that of the star. Submit My Answers Give Up Signed in as Kris Provide

Explanation / Answer

Given

Distance of a star from earth ds = 4500 ly

Power of quasar Lq = 43 Billion years times of Ls

Solution:-

Brightness B = L / (4*pi*d^2)

By Inverse Square Law,

Now,
Since Bs = Bq (as given)

So,

Ls / (4*pi*ds^2) = Lq / (4*pi*dq^2)

Ls / (4*pi*ds^2) = 43B*Ls / (4*pi*dq^2)

Here Ls/4*pi cancels on both sides

therefore

      1 /ds^2 = 43B / dq^2

=> dq^2 = 43B * ds^2

=> dq^2 = 43*10^9 * 4500^2

=> dq = 933139861 ly

=> dq = 9331.4*10^5 ly = 93.31*10^7 ly

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