The magnetic forces exerted by a permanent magnet are due to
A) electrons moving in atoms.
B) equal and opposite magnets placed on each of the two poles.
C) a miracle.
D) large-scale [macroscopic] electric currents on the surface of the magnet.
E) equal and opposite charges placed on each of the two "poles."
A
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The laws of physics demand that a neutron star has a maximum mass of ____ solar mass(es)
a. 1 b. 1.4 c. 3 d. 8 e. 20
The formula can be used to calculate a star's _____
a. mass b. distance c. rotation speed d. revolution period e. diameter
Scientists suspect that Mars once had abundant liquid water on its surface. For this to have been true, early Mars must have had ________ than Mars today.
A) a much higher atmospheric pressure and much stronger greenhouse effect B) a larger mass and radius C) a smaller axis tilt and less elliptical orbit D) larger polar caps and more dust storms
Which of the following elements has the most mass?
A) hydrogen B) iron C) lead D) uranium E) all have the same mass