2. The Systeme Internationale’ (SI) is the International Metric System There are 6 Base Units in the SI system 8/9/2011 Revision02 2 Base Units
3. The six basic units are not sufficient to act for all situations that arise in measurement. Derived units are used for all non-basic situations. Most derived units use the three basic units of length, mass and time in various combinations. . 8/9/2011 Revision02 3 SI Derived Units
4. 8/9/2011 Revision02 4 SI Derived Units The units used can be subdivided into three groups: mechanical, electrical and magnetic although it must be realised there are many more examples than those listed
7. In practical cases some SI values are inconveniently large or small, In order to choose values that are convenient to handle, multiples or submultiples are used. For example, if the resistance of an electrical installation is measured at 15 000 000 ohms, it is more convenient to refer to this value as 15 megohms. 8/9/2011 Revision02 7 Multiples And Submultiples
10. Another method of overcoming cumbersome rows of figures is to notate numbers to a value between 1 and 10 multiplied by 10 to some power. For example, 6 800 000 can be expressed as 6.8 x 106and 1250 as 1.25 x 103 8/9/2011 Revision02 10 Scientific Notation
11. Given: 1.015 x 10 -8 Answer: 0.00000001015 (8 places to left) Negative exponent move decimal to the left Given: 5.024 x 10 -3 Answer: 5,024 (3 places to the right) Positive exponent move decimal to the right 8/9/2011 Revision02 11 Examples:
12. Move decimal point to right for positive exponent of 10 Move decimal point to left for negative exponent of 10 8/9/2011 Revision02 12 To change from scientific notation to standard form:
13. Examples Express in standard form 1.09 x 10 3 4.22715 x 10 8 3.078 x 10 – 4 9.004 x 10 – 2 5.1874 x 10 2 8/9/2011 Revision02 13
