S.I. Units: Difference between revisions
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The modern metric system is the [https://en.wikipedia.org/wiki/International_System_of_Units '''International System of Units'''] ''(French: Système International d'Unités, SI)''. The system was published in 1960 and was based on the metre-kilogram-second system of units (MKS). There are now internationally agreed units covering all aspects of technology together with a set of prefixes which serve as multipliers or fractions of them. The preferred prefixes multiply or divide the unit names by 1000 ''(or 10<sup>-3</sup>)'' thus, 10mm is preferred to a centimetre, especially in construction and engineering. | The modern metric system is the [https://en.wikipedia.org/wiki/International_System_of_Units '''International System of Units'''] ''(French: Système International d'Unités, SI)''. The system was published in 1960 and was based on the metre-kilogram-second system of units (MKS). There are now internationally agreed units covering all aspects of technology together with a set of [https://en.wikipedia.org/wiki/Metric_prefix#List_of_SI_prefixes '''prefixes'''] which serve as multipliers or fractions of them. The preferred prefixes multiply or divide the unit names by 1000 ''(or 10<sup>-3</sup>)'' thus, 10mm is preferred to a centimetre, especially in construction and engineering. | ||
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Revision as of 15:32, 31 May 2015
The modern metric system is the International System of Units (French: Système International d'Unités, SI). The system was published in 1960 and was based on the metre-kilogram-second system of units (MKS). There are now internationally agreed units covering all aspects of technology together with a set of prefixes which serve as multipliers or fractions of them. The preferred prefixes multiply or divide the unit names by 1000 (or 10-3) thus, 10mm is preferred to a centimetre, especially in construction and engineering.
Note: Units named after people use capital letters for the letter symbol - but not for the unit name itself.
Measurement of Length
| Metre | ||||
| Prefix Name | Symbol | 10n | Decimal | Description |
| kilometre | km | 103 | 1000 | A thousand metres |
| metre | m | 100 | 1 | A metre |
| centimetre | cm | 10-2 | 0.01 | A hundredth of a metre |
| millimetre | mm | 10-3 | 0.001 | A thousandth of a metre |
| micrometre | μm | 10-6 | 0.000001 | A millionth of a metre |
Units used in Electronics
| Ohms (resistance) - named after Georg Simon Ohm | ||||
| Prefix Name | Symbol | 10n | Decimal | Description |
| mega-ohm | MΩ | 106 | 1000000 | A million ohms |
| kilo-ohm | kΩ (or K) | 103 | 1000 | A thousand ohms |
| ohm | Ω (or R) | 100 | 1 | An ohm |
| Note:
The unit or its prefix may be used to replace a decimal point - e.g. 2.2mega-ohm = 2M2; 2.2kilo-ohm = 2K2; and 2.2ohm = 2R2. | ||||
| Ampere (electric current)' - named after André-Marie Ampère | ||||
| Prefix Name | Symbol | 10n | Decimal | Description |
| ampere | A | 100 | 1 | Amp |
| milli-amp | mA | 10-3 | 0.001 | A thousandth |
| Farads (electric capacitance) - named after Michael Faraday | ||||
| Prefix Name | Symbol | 10n | Decimal | Description |
| farad | F | 100 | 1 | A Farad |
| micro-Farad | μF | 10-6 | 0.000001 | A millionth |
| nano-Farad | nF | 10-9 | 0.000000001 | A thousand millionth |
| pico-Farad | pF | 10-12 | 0.000000000001 | A trillionth |