UEENEEE003BSolve Problems in Single Path DC Circuits

Multiples, Sub Multiples and SI Units

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The Systeme Internationale’ (SI) is the International Metric System

There are 6 Base Units in the SI system

Base Units

Unit Symbol Quantity Symbol

Length l Metre m

Time s Second s

Mass m Kilogram kg

Current I Ampere A

Temperature T Kelvin K

Light I candela cd

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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. .

SI Derived Units

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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

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Derived Mechanical Units

Unit Symbol Quantity Symbol

Force F Newton N

Pressure P Pascal Pa

Energy & Work

W Joule J

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Derived Electrical Units

Unit Symbol Quantity Symbol

Power P watt W

Frequency F hertz Hz

Potential V volt V

Charge Q coulomb C

Capacitance C farad F

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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.

Multiples And Submultiples

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Multiples and Submultiples

Tera 1012 T

giga 109 G

mega 106 M

kilo 103 k

milli 10-3 m

micro 10-6 m

nano 10-9 n

pico 10-12 p

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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 106 and

1250 as 1.25 x 103

Scientific Notation

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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

Examples:

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Move decimal point to right for positive exponent of 10

Move decimal point to left for negative exponent of 10

To change from scientific notation to standard form:

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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

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Express in correct scientific notation

0.0000568

321

64 960 000

0.07085

61 500