What is the energy density in the magnetic field 25 cm from a long straight wire carrying a current of 12 A? (?0 = 4? × 10-7 T ? m/A)
A) 3.7 × 10-5 J/m3
B) 7.3 × 10-5 J/m3
C) 1.2 × 10-4 J/m3
D) 3.6 × 10-4 J/m3
E) The density cannot be determined without knowing the volume.
A
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Which best describes the relationship between two systems in thermal equilibrium?
a. no net energy is exchanged b. volumes are equal c. masses are equal d. zero velocity
Why won't Pluto collide with Neptune?
A) Pluto orbits the Sun exactly two times for every three Neptune orbits. B) Pluto is always much farther from the Sun than Neptune. C) Pluto's orbit never comes anywhere close to Neptune's orbit. D) Actually, a collision of the two is inevitable within the next billion years.
The Sun is gradually increasing in luminosity as it ages. It is about 30% more luminous than it was when it was born. Why isn't this increase considered to be an explanation for global warming?
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A girl is standing in front of a concave mirror. Consider two rays of light, one from her nose and one from her mouth that are parallel as they are traveling toward the mirror. These rays will come together:
a. at the focal point. b. at the center of curvature. c. at the image point. d. behind the mirror if she is too close to the mirror.