Base Units

Page 1

Kilogram

Base SI unit for measuring mass

Defined as the mass of a specific platinum-iridium alloy in France

Symbol: kg

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Metre

Base SI unit for measuring length

Defined as the distance travelled by light in 1/299792458 seconds

Symbol: m

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Second

Base SI unit for measuring time

Defined as exactly 9,192,631770 cycles of a Caesium atomic rock

Symbol: s

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Ampere

Base SI unit for measuring current

Defined as the current which if put through two parallel metre-long conductors places one metre apart in a vacuum, the force between them would be equal to 2 x 10^ -7 N

Symbol: A (Amps)

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Mole

Base SI unit for measuring the amount of a substance

Defined as the amount of a substance which contains the same number of particles as atoms in 12 grams of carbon-12

Symbol: mol

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Kelvin

Base SI unit for measuring temperature

The Kelvin scale is defined so the the triple point of water is at 273.6K; this is the temperature and pressure at which water exists as a gas, liquid, and solid together in thermodynamic equilibrium

Symbol: K

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Coulomb

Unit for measuring charge

Derived from the ampere and the second (1 coulomb is 1 ampere-second)

Symbol: C (As)

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Newton

Unit for measuring force

Derived from the kilogram, metre, and second (1 Newton is the force applied to a 1kg mass to cause it to accelerate at 1 metre per second squared)

Symbol: N (kgms^ -2)