We receive today the light from a distant galaxy and from its spectrum we conclude that it took 400 Myr for the photons to reach us. Which one of the following statements is correct? O The Universe is accelerating, so that galaxy is moving toward us at higher speed and it will take less than 400 Myr for future photons from that galaxy to reach us. O That galaxy is 400 million light years away from us today. O That galaxy is moving away from us, so today it is more distant from us than 400 million light years. O We are observing that galaxy as it was in the past, and today it is accelerating toward us.

We receive today the light from a distant galaxy and from its spectrum we conclude that it took 400 Myr for the photons to reach us. Which one of the following statements is correct? O The Universe is accelerating, so that galaxy is moving toward us at higher speed and it will take less than 400 Myr for future photons from that galaxy to reach us. O That galaxy is 400 million light years away from us today. O That galaxy is moving away from us, so today it is more distant from us than 400 million light years. O We are observing that galaxy as it was in the past, and today it is accelerating toward us.

Astronomy

1st Edition

ISBN:9781938168284

Author:Andrew Fraknoi; David Morrison; Sidney C. Wolff

Publisher:Andrew Fraknoi; David Morrison; Sidney C. Wolff

Chapter27: Active Galaxies, Quasars, And Supermassive Black Holes

Section: Chapter Questions

Problem 27E: In the Check Your Learning section of Example 27.1, you were told that several lines of hydrogen...

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(a) What is the approximate speed relative to us of a galaxy near the edge of the known universe, some 10 Gly away? (b) What traction of the speed of light is this? Note that we have observed galaxies moving away from us at greater than 0.9c.
(a) Wliat is the approximate velocity relative to us of a galaxy near the edge of the known universe, some 10 Gly away? (b) What fraction of the speed of light is this? Note that we have observed galaxies moving away from us at greater than 0.9c.
In the Check Your Learning section of Example 27.1, you were told that several lines of hydrogen absorption in the visible spectrum have rest wavelengths of 410 nm, 434 nm, 486 nm, and 656 nm. In a spectrum of a distant galaxy, these same lines are observed to have wavelengths of 492 nm, 521 nm, 583 nm, and 787 nm, respectively. The example demonstrated that z=0.20 for the 410 nm line. Show that you will obtain the same redshift regardless of which absorption line you measure.
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If we were to analyze the magnetic flux lines of a current-carrying conductor, oriented perpendicularly to a magnetic field between two bar magnets, the interaction would look something like this: S N S N This interaction of magnetic flux lines (the bar magnets' straight lines versus the wire's cireles) will produce a mechanical force on the wire (called the Lorentz force). Which direction will this force act? Also, determine the direction of current through the conductor (seen from an end-view in the above illustration) necessary to produce the circular magnetic flux shown.
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