How are galaxies important to our existence?
A) Deep in their centers, galaxies created the elements from which we are made.
B) Galaxies recycle material from one generation of stars to the next, and without this recycling we could not exist.
C) Without galaxies, the universe could not be expanding.
D) Without galaxies, there could not have been a Big Bang.
B
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A wire of a certain length is carrying a current of 2.0 A. It is placed at an angle of 60° with respect to a magnetic field of strength 0.20 T. If the wire experiences a force of 0.40 N, what is the length of the wire?
A) 1.0 m B) 1.2 m C) 1.4 m D) 1.6 m E) 1.8 m
A stars exhibit strong hydrogen absorption lines because the surface temperature of 10,000 K is high enough to place most hydrogen in an excited, but not yet ionized, state
The transitions from this excited state then correspond to visible light wavelengths. Which of the following statements is a plausible explanation for why G stars exhibit weak hydrogen absorption lines? A) G stars contain very little hydrogen. B) At these high temperatures, nearly all the hydrogen is ionized, and unable to interact with light. C) G stars are too cool to excite hydrogen atoms to the first energy level from which they can then absorb visible wavelengths of light.
Consider a solid cube with a uniform internal charge density ?0. What kind of field does this cube create?
A. Unidirectional B. Axial C. Radial D. None of the above
The ratio of the density of a material to the density of water is
a. the mass density. b. the weight density. c. the specific gravity. d. the buoyant force. e. none of the above.