The si unit of length, the meter, is currently defined a) 1,553,164.1 wavelengths of red cadmium light in dry air at 25°c. b) by the president's foot. c) as the length of the path traveled by light in a vacuum during 1/299792485 s. 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) as 10-7 of the distance from the north pole to the equator along a meridian running through paris. 2) the si unit of mass, the kilogram, is currently defined a) as 10-22 the mass of the earth's moon. b) by a prototype platinum-iridium cylinder kept at the international bureau of weights and measures in sevres, france. c) by the president's weight. d) the mass of 5.9786332 × 1026 protons. e) as 10-24 the mass of the earth. 3) the si unit of time, the second, is currently defined by a) the time required for light to travel 1/299,792,458 of a meter. b) the rotation period of the earth. c) a standard clock at the international bureau of weights and measures in france. d) the motion of the earth in orbit. e) a duration of an atomic clock. 4) four students measure the mass of an object, each using a different scale. they record their results as follows: which student used the least precise scale? a) a b) b c) c d) d e) the precision of all scales were equal