1. International System of Units Flashcards
Define “international system of units”
It’s the modern metric system of measurement. There are two classes of SI units.
What are the two classes of SI units?
Basic units = time, length, mass, electric current, thermodynamic temp, luminous intensity and amount of substance)
Derived units = area, volume, velocity, acceleration, wavenumber, density, specific volume, current density, magnetic field strength, substance concentration and luminance
How is “time” measured?
Seconds (s)
The second is the duration of: 9, 192, 631 and 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.
How is “length” measured?
Meters (m)
The meter is the length of the distance travelled by light in vacuum during a time interval of 1/299 792 458th of a second.
How is “mass” measured?
Kilogram (kg)
The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram.
How is “electric current” measured?
Ampere (A)
The Ampere is that CONSTANT current which, if maintained in two straight parallel conductors of infinite length, of negotiable circular cross-section, and placed 1 meter apart in a vacuum, would produce between these conductors a force equal to 2x10E-7 Newton per meter of length.
How is “thermodynamic temperature” measured?
Kelvin (K)
The Kelvin, unit of thermodynamic temp, is the fraction 1/273.16 of the thermodynamic temp of the “triple point of water”
How is “luminous intensity” measured?
Candela (cd) aka “Candle”
The Candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency = 540x10E12 Hertz AND has a radiant intensity in that direction of 1/683 watt per steradian
How is “amount of substance” measured?
mole (mol)
The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kg of the weighed substance.
