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SI Prefixes

  1. Jun 5, 2008 #1
    Are there prefixes for the decimal places in between the ones that are commonly used?

    Like for 10^-4, or 10^-7?
     
  2. jcsd
  3. Jun 5, 2008 #2

    D H

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    There are SI prefixes for 100, 10, 1/10, and 1/100. Above/below that, all prefixes reference powers of 1000.
     
  4. Jun 5, 2008 #3
    1000m 10n Prefix Symbol Since[1] Short scale Long scale Decimal
    10008 1024 yotta- Y 1991 Septillion Quadrillion 1 000 000 000 000 000 000 000 000
    10007 1021 zetta- Z 1991 Sextillion Trilliard 1 000 000 000 000 000 000 000
    10006 1018 exa- E 1975 Quintillion Trillion 1 000 000 000 000 000 000
    10005 1015 peta- P 1975 Quadrillion Billiard 1 000 000 000 000 000
    10004 1012 tera- T 1960 Trillion Billion 1 000 000 000 000
    10003 109 giga- G 1960 Billion Milliard 1 000 000 000
    10002 106 mega- M 1960 Million 1 000 000
    10001 103 kilo- k 1795 Thousand 1 000
    10002/3 102 hecto- h 1795 Hundred 100
    10001/3 101 deca- da 1795 Ten 10
    10000 100 (none) (none) NA One 1
    1000−1/3 10−1 deci- d 1795 Tenth 0.1
    1000−2/3 10−2 centi- c 1795 Hundredth 0.01
    1000−1 10−3 milli- m 1795 Thousandth 0.001
    1000−2 10−6 micro- µ 1960[2] Millionth 0.000 001
    1000−3 10−9 nano- n 1960 Billionth Milliardth 0.000 000 001
    1000−4 10−12 pico- p 1960 Trillionth Billionth 0.000 000 000 001
    1000−5 10−15 femto- f 1964 Quadrillionth Billiardth 0.000 000 000 000 001
    1000−6 10−18 atto- a 1964 Quintillionth Trillionth 0.000 000 000 000 000 001
    1000−7 10−21 zepto- z 1991 Sextillionth Trilliardth 0.000 000 000 000 000 000 001
    1000−8 10−24 yocto- y 1991 Septillionth Quadrillionth 0.000 000 000 000 000 000 000 001

    Shamelessly taken from wiki.
     
  5. Jun 5, 2008 #4

    LURCH

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    None of which I am aware. For 10-4, you just say ".1 milli" or "100 micro," and on like that.
     
  6. Jun 5, 2008 #5

    nicksauce

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    There are a few odd ones, for example 10^-10 m is an angstrom, or 1 Tesla = 10000 Gauss.
     
  7. Jun 5, 2008 #6

    mgb_phys

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    The angstrom is an unofficial 'convenient' unit like the barn so doesn't fit in the SI series.
    The Gauss / Tesla is because of the switch from cgs to mks units.

    The centi / hecto were just because people had traditionally been used to working in units of 100 - at least outside Britain!

    The annoying one is the kilogram, either the gram should have been redefined (messy) or a new name chosen so that the base unit of mass didn't have a prefix.
     
  8. Jun 5, 2008 #7
    I have always wondered this! All units (at least the ones I ever saw) in the SI system use the kilogram instead of the gram. For example, a Newton is a kilogram-meter per second^2.
    Why not a gram-meter per second^2? All other units are the 'base' units without kilo, milli, whatever as a prefix...

    Is it just because the kilogram is so common (where I live anyway), or is there another reason?
     
  9. Jun 5, 2008 #8

    mgb_phys

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    Originally units were defined in terms of centimetre/gram/second, I have no idea why the cm was chosen except that it was a convenient human size unit like the inch.
    It took around 100years before MKS replaced them in the 1950s

    Unfortunately this was a 100 years in which quite a lot was invented - including all of electromagnetism. Just to make it even more fun, a lot of the electromagnetic units differ by factors like 2pi and 4pi between cgs and mks as well as the factors of 1000 you would expect. Although pretty much textbooks are now mks, a lot of papers especially in astronomy and chemistry use cm or 1/cm.

    Just like a Tesla is a new name rather than calling the base unit 10KGauss they really should have come up with a new name for the kilo.
    They didn't becuase it is the unit most widely used outside of science, so although Gauss and Tesla are used together in electrical engineering today it would be very confusing in shops if you had grams and whatever the new unit was called ( and pounds!)
     
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