In a region of space where the electric field is radial, suppose that Er = C/r3, where C is a positive constant. Is the charge density ? in this region positive, negative, or zero? (Note: ? might depend on r in this region.)
A. Positive
B. Negative
C. Zero
D. This is impossible.
B. Negative
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Which of the following statements is true of reflection nebulae?
A) They have a distinctive blue color. B) The gases in reflection nebulae are excited to emit photons. C) The spectrum of a reflection nebula is not the reflected absorption spectrum of starlight. D) They are produced when a hot star excites the gas to produce an emission spectrum.
Induction: Two uncharged metal spheres, #1 and #2, are mounted on insulating support rods. A third metal sphere, carrying a positive charge, is then placed near #2. Now a copper wire is momentarily connected between #1 and #2 and then removed. Finally, sphere #3 is removed. In this final state
A. spheres #1 and #2 are still uncharged. B. sphere #1 carries positive charge and #2 carries negative charge. C. sphere #1 carries negative charge and #2 carries positive charge. D. spheres #1 and #2 both carry positive charge. E. spheres #1 and #2 both carry negative charge.
Force on a Wire: A 2.0-m straight wire carrying a current of 0.60 A is oriented parallel to a uniform magnetic field of 0.50 T. What is the magnitude of the magnetic force on it?
A. zero B. 0.15 N C. 0.30 N D. 0.60 N
What is the angular momentum of the moon about the Earth? The mass of the moon is 7.35 × 10^22 kg, the center-to-center separation of the Earth and the moon is 3.84 × 10^5 km, and the orbital period of the moon is 27.3 days. Ignore the small offset of the center of mass of the system from the center of the Earth in your calculation