The diameter of no. 12 copper wire is 0.081 in. The maximum safe current it can carry (in order to prevent fire danger in building construction) is 20 A
At this current, what is the drift velocity of the electrons? (The number of electron carriers in one cubic centimeter of copper is 8.5 × 1022.) A)
0.044 mm/s
B)
0.44 mm/s
C)
0.44 cm/s
D)
0.44 m/s
E)
4.4 m/s
B
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A uniform rod (mass = 1.5 kg) is 2.0 m long. The rod is pivoted about a horizontal, frictionless pin through one end. The rod is released from rest in a horizontal position. What is the angular speed of the rod when the rod makes an angle of 30° with the horizontal? (The rotational inertia of the rod about the pin is 2.0 kg?m2).
A. 2.2 rad/s B. 3.6 rad/s C. 2.7 rad/s D. 3.1 rad/s E. 1.8 rad/s
Satellite Motion: Suppose our sun had 4 times its present mass but the earth orbited it at the same distance as it presently does. What would be the length of the year on the earth under those conditions?
A. 1/4 as long as the present year B. 1/2 as long as the present year C. the same as the present year D. twice as long as the present year E. four times as long as the present year
Interactions among galaxies also are thought to influence a galaxy's type in at least some cases. Which of the following does not support the idea that interactions can shape galaxies?
A) the fact that more distant galaxies have larger redshifts B) computer modeling of collisions between galaxies C) the fact that galaxies with distorted appearances are more common at great distances than nearby D) the presence of features such as "tails" extending out of galaxies, bridges between galaxies, and rings of stars around galaxies
A guitar is perfectly tuned. The tension on its strings is then increased. Which of the following is true?
A. The speed of sounds from the guitar is larger than before B. The frequencies of sounds from the guitar are higher than before C. The wavelengths of sounds from the guitar are longer than before D. The amplitudes of sounds from the guitar are larger