Magnetic fields are produced by
a. constant electric currents.
b. electric currents that vary sinusoidally with time.
c. time-varying electric fields.
d. all of the above.
e. only (a) and (b) above.
d
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Approximately how long does the protostellar stage last for a starlike our Sun?
A) 300 years B) 30,000 years C) 100,000 years D) 30 million years E) 30 billion years
As a star forms, the photosphere first appears:
A) when the planetary nebula is expelled. B) when the protostar forms. C) when contraction slows down. D) when nuclear fires ignite. E) when the star reaches the main sequence.
To orient the LCMs of a polymer, it must be rapidly deformed just above the _________transition temperature and below the melting temperature.
Fill in the blank(s) with the appropriate word(s).
Bullet G is dropped, from rest, at the same time that another bullet H is fired horizontally from a rifle. If both bullets leave from the same height above the ground, then
A) bullet G hits the ground before bullet H does. B) both bullets hit the ground at the same time. C) bullet H hits the ground before bullet G does. D) not enough information is given to compare when they hit.