31_SI_UNITS

• Building Services
• Further Education (Key Stage 5)

What are you going to learn?

In this lesson you're going to learn about SI units

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What are the SI 

Units

Basic SI units

The Electrical SI

Units

Basic SI units, multiples & unit conversion

SI units

Over the years it has become increasingly obvious that when trying to understand one another it is better that a common form of expression is adopted, particularly when engineers, scientists etc. need to communicate. If there was no common understanding a large number of differing standard forms would be adopted making conversion of units difficult.

Defintion of SI Units

^{This system of common identification of units is called Systeme Internationale d’unities, shortened to SI units.}<div>
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Number of SI Units

There are seven fundamental units and of these it is only necessary for us to remember five of them.
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SI Units

Five Basic SI Units

<ol><li>Length&nbsp; (m)</li><li>Mass&nbsp; &nbsp; &nbsp; (Kg)</li><li>Time&nbsp; &nbsp; &nbsp; (sec)</li><li>Current (Amp)</li><li>Temperature (Kelvin)</li></ol><div><br></div>

The seven SI base units

<ol><li>Length - meter (m)
</li><li>Time - second (s)
</li><li>Amount of substance - mole (mole)
</li><li>Electric current - ampere (A)
</li><li>Temperature - kelvin (K)
</li><li>Luminous intensity - candela (cd)</li><li>Mass - kilogram (kg)</li></ol>

SI Basic Units

Size of Units

5000 watts is Equivalent To

Text

1. 5KW
2. 5MW
3. 5TW
4. 5GW

2500000VA

1. 25KVA
2. 2.5GVA
3. 0.25GVA
4. 2.5MVA

Conversion Table

7 x 1000

1. 7⋅10​3​​
2. 7⋅10​4​​
3. 7⋅10​6​​
4. 7.10​0​​