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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Galactic disks appear blue because:
A) they contain no G, K, or M dwarfs. B) they contain only blue reflection nebulae. C) dust obscures the longer, red, wavelengths. D) O and B blue giants are much brighter than G, K, or M dwarfs. E) dark matter gravitationally shifts all wavelengths towards the blue.
A truck is carrying a 120-kg refrigerator, which is 2.20 m tall and 85.0 cm wide has its center of mass at its geometrical center
The refrigerator is facing sideways and a short strip on the bed of the truck keeps the refrigerator from sliding. What is the maximum acceleration that the truck can have before the refrigerator begins to tip over? A) 1.90 m/s2 B) 4.17 m/s2 C) 3.79 m/s2 D) 7.58 m/s2 E) 8.34 m/s2
A 5.00-kg object moves clockwise around a 50.0 cm radius circular path. At one location, the speed of the object is 4.00 m/s
When the object next returns to this same location, the speed is 3.00 m/s. (a) How much work was done by non-conservative forces as the object moved once around the circle? (b) If the magnitude of the above non-conservative forces acting on the object is constant, what is the minimum value of this magnitude?
Plate tectonics states that
A) the continents move through Earth's crust like an icebreaker through ice. B) earthquakes occur because tectonic plates break like a dropped dinner plate. C) tectonic plates have not moved since Pangaea broke up. D) tectonic plates are in slow, but constant motion.