What evidence suggests that most of the mass of the Milky Way is in the form of dark matter?
A) The orbital speeds of stars far from the galactic center are surprisingly high.
B) Theoretical models of galaxy formation suggest that a galaxy cannot form unless it has at least 10 times as much matter as we see in the Milky Way disk.
C) Although dark matter emits no visible light, we have detected its radio emissions.
D) Our view of distant galaxies is often obscured by dark blotches, which are presumably made of dark matter.
A
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By what factor is the resistance of a copper wire changed when its temperature is increased from 30.0°C to 115°C? The temperature coefficient of resistivity for copper = 3.9 × 10^?3 (°C)?1
a. 1.45 b. 1.12 c. 1.33 d. 0.669 e. 4.32
A long wire carries a current toward the north in a magnetic field that is directed vertically downward. What is the direction of the magnetic force on the wire?
a) west b) north c) east d) vertically upward e) vertically downward
A heater draws 20A when connected to a 110-V line. If the electric power costs 20 cents per kilowatt hour, the cost of running the heater for 10 hours is
A) $0.44. B) $1.10. C) $4.40. D) $11.00. E) none of the above
American power plants usually supply 120. volts AC:
(a) at what frequency? (b) at what maximum voltage?