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Back to Measurement Units

These are some of the things that we measure in everyday living. *  time                                *   distance or length            *  speed *  temperature                   *   area                                 *   money *  mass                               *   volume                             * capacity To measure quantities like this, units of measurement are required. The system of units we use in Australia is called the metric system. Calculations in metric system is easy, because they are based on powers of 10 just like in our decimal system. The following units are most commonly used and it is important to remember their symbols(or shortened form). Quantity Name of unit Symbol Value length millimetre centimetre metre kilometre mm cm m km 10mm   = 1cm 100cm  =  1m 1000m  =  1km mass milligram gram kilogram tonne mg g kg t 1000mg = 1g 1000g  = 1kg 1000kg = 1t time second minute hour day s min h day 60s = 1min 60min = 1h 24h = 1day temperature degrees Celcius °C area square millimetre square centimetre square  metre hectare   volume cubic millimetres cubic centimetres cubic metres capacity (volume of fluids) millilitre litre kilolitre mL L kL 1000ml = 1 L 1000L  = 1kL speed metres per second kilometres per hour Units in blue are standard units. Remember ! To convert small units into large units you divide. ( ÷ ) To convert large units to small units you multiply. ( × )   In Engineering and in Sciences, we use very larger units as well as very smaller units. Here are the some of the prefixes and the symbols and their values.

 

 

 

 

Examples

(1) Let's convert 250cm to metres.      100cm  =  1m      250cm  =  250 ÷ 100                  =   2.5m centimetre(cm) is the smaller unit than the metre, so to convert smaller unit to a larger unit we divide. 100cm = 1m , we divide by 100. (2) Let's convert 2.8kg to grams.       1kg    =   1000g       2.8kg =   2.8 × 1000                 =   2800g kilogram is the larger unit than the gram, so to convert larger unit to a smaller unit, we multiply by the factor. 1kg = 1000g, we multiply by 1000. (3) Let's convert 100milliamperes(mA) to              amperes(A)      1000mA = 1A       100mA  = 100 ÷ 1000                     = 0.1A                                  milliampere(mA) is the smaller unit than the ampere(A), so to convert smaller unit to a larger unit we divide by the factor.1000mA = 1A, we divide by1000. In Engineering and in Sciences we use scientific notation for cacculations. Instead of the term "milli" we can put 10-3

 

 

 

 

 

 

Have a Go Problem 1  Convert: (a) 180 cm to metres (m) (b) 1.5 minutes to seconds(sec) (c) 250 milligrams(mg) to grams       Problem 2 Convert: (a) 300 millivolts (mV) to volts (b) 2800 megavolts to volts (c) 0.002amperes(A) to      microamperes(µA)

 

 

 

 

 

 

Practice Questions Question 1 Convert 1500ml to litres.     Answer 1.5 L Question 2 Convert 90sec to minutes.     answer 1.5 min   Question 3 Convert 2.25km to centimetres.   answer 225000 cm   Question 4 Convert 1750g to kilograms.   answer 1.750 kg   Question 5 The current of a circuit is 5 ×10-5 A. Convert this current to microamperes.   answer 50 micro amps   Question 6 Convert 1000 000 Watts to megawatts.   answer 1 MW

 

 

 

 

 

 

Solution 1 (a) 180cm to metres      100cm = 1m      180cm = 180 ÷ 100                 = 1.8m Remember: smaller units to larger units you divide(÷) (b) 1.5 minutes to seconds(sec)       1min  =  60 sec       1.5min = 1.5 × 60                  = 90 sec larger units to smaller units you multiply(×) (c) 250mg to grams      1000mg = 1g        250mg = 250 ÷ 1000                   = 0.250g smaller units to larger units you  divide (÷) when dividing by 1000 you move the decimal point in 250.0, three places to the left.     back to Have a Go

Solution 2 (a) 300mV to V      method 1      300mV = 300 × 10-3                  = 3×102 × 10-3                       = 3× 10-1                       = 0.3 V     method 2     300mV = 300 ÷ 1000                  = 0.3 V method 1 Remember: Instead of "milli" we can put " 10-3 " method 2 1000mV = 1 V smaller units to larger units you  ÷ , when dividing by 1000 you move the decimal point in 300.0, three places to the left. (b) 2800MV to V            1MV = 106 V      2800MV = 2800 × 106 V                     = 2.8 × 103 × 106 V                     = 2.8 × 109 V Remember: Instead of "mega" we can put " 106 " (c) 0.002A to microamperes(µA)            1 A = 106 µA      0.002A = 0.002 × 106 µA                   = 2 × 10-3 × 106 µA                   = 2 × 103 µA                   = 2000 µA microampere the smaller unit, ampere the larger unit, A to µA that is larger to smaller units you muutiply (×)   back to Have a Go

 

 

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