Earth's magnetic field is generated by the dynamo effect in the
a. molten metallic core.
b. solid central core.
c. plastic mantle.
d. crust.
e. aurora.
a
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A system consists of two very large thermal reservoirs in contact with each other, one at temperature 300°C and the other at temperature 200°C
When 600 J of heat transfers from the 300°C reservoir to the 200°C reservoir, what is the change in entropy of this system? A) 0.221 J/K B) 1.00 J/K C) 5.00 J/K D) -1.00 J/K E) -2.31 J/K
On a hot day, molecules of air ________ than on a cold day.
A) move faster on average B) move slower on average C) are more massive D) are less massive E) contain more atoms
Imagine that in a certain region of space, an electric field is uniform in magnitude and direction. What can we conclude about the magnetic field in that region?
A. 
= 0.
B. must be uniform in space.
C. must be constant in time.
D. must be both uniform in space and constant in time.
E. There are no restrictions on .
F. There are other restrictions on (specify).
A composite beam of aluminum (Ea 5 72 GPa) and steel (Es 5 190 GPa) has a width b 5 25 mm and heights ha 5 42 mm and hs 5 68 mm, respectively. A bending moment is applied about the z axis resulting in a maximum stress in the aluminum of 55 MPa. The maximum stress in the steel is approximately:
(A) 86 MPa
(B) 90 MPa
(C) 94 MPa
(D) 98 MPa