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Metric Unit Prefixes

Page history last edited by David Young 6 years, 2 months ago

The SI System of Measurement

 

SI units (Le Systeme International d’Unites) – or more commonly called the metric system – was adopted for scientific research in 1960 worldwide, and is used as general measurement in most countries (USA excepted).

 

Fundamental SI Units

 

  • cannot be measured in simpler form, these are the most basic quantities

  • derived units are based on the measurement of two or more fundamental quantities.  For example, speed is determined from measurements of distance and time.  The unit for speed (m/s or km/hr) is derived from these quantities.

     

 

DEFINE - SI or metric unit prefixes are added to units to express larger and smaller unit values.  For example the prefix "kilo" means 1000.  A "kilo"meter is the equivalent of 1000 meters.  Unit prefixes are used in the same way as scientific notation to make large and small numbers more manageable.  For example, the average distance to the Moon from the Earth is about 384403000 m - about 3.8 x 108 m.  Instead of using scientific notation this value could be written as:

384403 km      "kilo" = x 103

or

384.403 Mm     "mega" = x 106

 

A list of some common unit prefixes is shown in the table below:

 


USE - Many calculations require you to make conversions between metric prefixes to obtain the correct answer.  In physics, common calculations require you to work in meters, kilograms and seconds.  Chemistry applications commonly use grams for mass.  Part of a good problem solving strategy is to remember to check to see if unit conversions are necessary after identifying values but before doing calculations.  For these reasons, it is beneficial to be skilled at conversions between metric prefixes.

 

EXAMPLES - Watch the video below to work through the following examples.   This video looks at the power of 10 represented by each prefix to determine how to move the decimal point when making conversions.

 

  1. 7000 ohms = _____________ kilo-ohms
  2. 600 mA = _____________ A
  3. 4800 V = _____________ kV
  4. 0.0065 mW = ___________ uW
  5. 750 000 000 pF = ___________ uF
  6. 2.4 GHz = ____________ kHz

 

 

Converting between different metric unit prefixes :  

 

 

REMEMBER -   If the unit converted is getting larger, the number value decreases. 

If the unit converted is getting smaller, the number value increases!

 

      

 

USEFUL HINT - Most calculations that require unit conversions usually involve converting a prefixed unit to the base unit.  Two common examples include converting km to m (in physics) and kg to g (in chemistry).  Whenever a prefixed unit is given and the base unit is required, it is much quicker to just enter the measurement into the calculator using scientific notation.

 

For example, the given value is 354 kg, you require g.  Enter the value into the calculator as 354 x 103.  By adding the power of 10 multiplier for kilo (103), you are now working in grams.

 

On your calculator:  Press [3] [5] [4], Press [2ND] [EE], Press [3]

 

 

 

 

 

 

INDEX

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