The SI unit of length, the meter, is currently defined
A) as 10-7 of the distance from the North Pole to the equator along a meridian running through Paris.
B) as the length of the path traveled by light in a vacuum during 1/299792485 s.
C) by the President's foot.
D) as the distance between two marks on a metal bar make of a platinum-iridium alloy kept at the National Bureau of Standards.
E) 1,553,164.1 wavelengths of red cadmium light in dry air at 25°C.
B
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In what direction does Uranus orbits the Sun?
A. It orbits the Sun in the opposite direction as the other planets. B. It orbits the Sun in the same direction as the other planets.
How did Edwin Hubble measure the distance to the Andromeda Galaxy?
A) He measured its parallax. B) He applied the period-luminosity relation to Cepheid variables. C) He deduced it from its redshift. D) He used white dwarf supernovae.
What do sunspots, solar prominences, and solar flares all have in common?
A) They all occur only in the Sun's photosphere. B) They are all shaped by the solar wind. C) They are all strongly influenced by magnetic fields on the Sun. D) They all have about the same temperature.
Wire B has twice the length and twice the radius of wire A. Both wires are made from the same material. If wire A has a resistance R, what is the resistance of wire B?
1. 4R 2. 2R 3. R 4. ½ R 5. ¼ R