Which of the following is the direction of an electromagnetic wave having electric and magnetic vectors E and B?
A. E
B. B
C. E·B
D. 
E. 
D.
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Which of the following best describes a set of conditions under which archaeoastronomers would conclude that an ancient structure was used for astronomical purposes?
A) The structure has holes in the ceiling that allow viewing the passage of constellations that figure prominently in the culture's folklore, and many other structures built by the same culture have ceiling holes placed in the same way. B) They find that, looking out from the center of the building, there are two windows that align with the rise and set points of two bright stars. C) The structure has 29 straight lines pointing out from a center, just like there are 29 days in the lunar cycle. D) The structure has the same dome shape as modern astronomical observatories.
The electric potential at the surface of a charged conductor
a. is always zero. b. is always independent of the magnitude of the charge on the surface. c. may be set equal to zero by adding an appropriate constant to the potential at all points of space. d. is always such that the potential is zero at all points inside the conductor. e. is always such that the potential is always zero within a hollow space inside the conductor.
When the reflection of an object is seen in a convex mirror the image will:
a. may be either real or virtual. c. always be virtual. b. will always be enlarged. d. always be real.
The stars in our sky twinkle in brightness and color because of
A) turbulence in the Earth's atmosphere. B) rapid changes in the brightnesses and colors of stars caused by changes in their spectra. C) light pollution. D) the bubbling and boiling of gases on the surfaces of stars.