A 25.0-mH inductor is connected in series to a 20.0-? resistor through a 15.0-V dc power supply and a switch. If the switch is closed at t = 0 s, what is the time constant of this circuit?
A) 0.800 × 10-3 s
B) 0.800 × 10-2 s
C) 0.500 s
D) 1.25 × 10-3 s
E) 12.5 × 10-2 s
D
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Consider the segment of cylindrical metal wire shown below. Assume that the drift speed of electrons is everywhere the same in the segment. Note that area B is tilted so that its nose vector makes an angle of ? < 90° with the drift velocity direction but still spans the wire’s entire cross section. How do the current density fluxes through areas A and B compare?
A. The flux through A is greater than the flux through B.
B. The flux through B is greater than the flux through A.
C. The fluxes through A and B are the same.
The best way to use a telescope to look for life on other planets is to
a. search for absorption from nitrogen in their atmospheres. b. search for absorption from oxygen in their atmospheres. c. search for emission lines from water vapor in their atmospheres. d. search for carbon dioxide on their moons.
Suppose that we have a sample of 20 atoms of radioactive potassium which decays by half every 1.3 billion years into calcium and argon at ratios of 9:1, respectively. How many atoms of calcium do you expect to find in this sample after 1.3 billion years?
A. 9 B. 18 C. 1 D. 2
If a force always acts perpendicular to an object's direction of motion, that force cannot change the object's kinetic energy
A) True B) False