Why can't we see past the cosmological horizon?
A) The universe extends only to this horizon.
B) Beyond the cosmological horizon, we are looking back to a time before the universe had formed.
C) We do not have telescopes big enough.
D) We do not have sensitive enough detectors.
E) The cosmological horizon is infinitely far away, and we can't see to infinity.
B
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A power line carries 1000 A at a height of 20 m above the ground. What is the resulting magnetic field at ground level?
A. 50 mT
B. 0.13 mT
C. 13 
T
D. 10 
T
E. 5.0T
What evidence do we have that the center of our galaxy contains magnetic fields?
What will be an ideal response?
How are galaxies important to our existence?
A) Without galaxies, there could not have been a Big Bang. B) Without galaxies, the universe could not be expanding. C) Deep in their centers, galaxies created the elements from which we are made. D) Galaxies recycle material from one generation of stars to the next, and without this recycling, we could not exist.
When one observes a scratch on the bottom of a block of clear plastic, the scratch appears to be 2.5 cm below the top surface as viewed from above. The actual thickness of the plastic block is 3.0 cm. The index of refraction of the block is ________.
Fill in the blank(s) with the appropriate word(s).