18. A cubic box with an edge of exactly 1 cm has a volume of:
A) 10–9 m3
B) 10–6 m3
C) 10–3 m3
D) 103 m3
E) 106 m3
19. A square with an edge of exactly 1 cm has an area of:
A) 10–6 m2
B) 10–4 m2
C) 10-2 m2
D) 102 m2
E) 104 m2
20. The SI standard of length is based on:
A) the distance from the north pole to the equator along a meridian passing through Paris
B) wavelength of light emitted by Hg198
C) wavelength of light emitted by Kr86
D) a precision meter stick in Paris
E) the speed of light
21. Which of the SI standard units is NOT based on a constant of nature?
A) The meter, because the speed of light can vary from place to place.
B) The second, because cesium cannot be found everywhere.
C) The kilogram, because it is based on an arbitrary piece of metal.
D) The kilogram, because the gram is the standard unit.
E) The meter, because it is defined in terms of the speed of light in vacuum, and there is no
perfect vacuum anywhere.