8/2/2019 NMMU ENG1 Section1A Rev2

1/13

ELECTRICAL ENGINEERING I(ENG131)

SECTION 1

QUANTITIES AND APPLICATIONS(A) Conversion of Units

8/2/2019 NMMU ENG1 Section1A Rev2

2/13

SISYSTEM OF UNITS

Length - meter (m)

Mass - kilogram (kg)

Force - Newton (N)

Temperature - Kelvin (K)

Energy - Joule (J) Time - second (s)

8/2/2019 NMMU ENG1 Section1A Rev2

3/13

PREFIXES FOR USE WITH

SIUNITS (> unit)

Prefix Symbol Relationship to Primary Unit

Yotta Y UNIT x 1024 or x 1 000 000 000 000 000 000 000 000

Zetta Z UNIT x 1021 or x 1 000 000 000 000 000 000 000

Exa E UNIT x 1018

or x 1 000 000 000 000 000 000Peta P UNIT x 1015 or x 1 000 000 000 000 000

Tera T UNIT x 1012 or x 1 000 000 000 000

Giga G UNIT x 109 or x 1 000 000 000

Mega M UNIT x 106

or x 1 000 000kilo k UNIT x 103 or x 1 000

hecto h UNIT x 102 or x 100

deca da UNIT x 101 or x 10

UNIT UNIT x 100

or x 1

8/2/2019 NMMU ENG1 Section1A Rev2

4/13

PREFIXES FOR USE WITH

SIUNITS (< unit)

Prefix Symbol Relationship to Primary Unit

UNIT UNIT x 100 or x 1

deci d UNIT x 10-1 or x 0.1

centi c UNIT x 10-2 or x 0.01

milli m UNIT x 10-3 or x 0.001

micro UNIT x 10-6 or x 0.000 001

nano n UNIT x 10-9 or x 0.000 000 001

pico p UNIT x 10-12 or x 0.000 000 000 001

femto f UNIT x 10-15 or x 0.000 000 000 000 001

atto a UNIT x 10-18 or x 0.000 000 000 000 000 001

zepto z UNIT x 10-21 or x 0.000 000 000 000 000 000 001

yocto y UNIT x 10-24 or x 0.000 000 000 000 000 000 000 001

8/2/2019 NMMU ENG1 Section1A Rev2

5/13

CONVERSION BETWEEN

LEVELS OF POWERS OF 10

Often necessary to convert from one

power of 10 to another for calculations

or graphical plots

You MUST know your prefixes to

enable you to determine what

multiplying factor required

8/2/2019 NMMU ENG1 Section1A Rev2

6/13

CONVERSION BETWEEN

LINEAR, SQUARE & CUBE

Many calculations require use of linear(m), square (m2) and cubic (m3) units

Values often not expressed in theseunits, ie. conductor cross-sectional area(csa) expressed in mm2 and

liquid/metal/gas volume expressed incm3 or litre

Values in formulas should be expressedas m, m2 or m3, therefore conversion

required

8/2/2019 NMMU ENG1 Section1A Rev2

7/13

8/2/2019 NMMU ENG1 Section1A Rev2

8/13

8/2/2019 NMMU ENG1 Section1A Rev2

9/13

CONVERSION BETWEEN

LINEAR UNITS

EXAMPLE 1

Linear units:

Convert 1520 mm to m

Multiply by 10-3 or move decimal point 3

places to the left

1520 mm = 1520 x 10-3 m or 1.52 m

8/2/2019 NMMU ENG1 Section1A Rev2

10/13

CONVERSION BETWEEN

SQUARED UNITS

Procedure for conversion of squared valuefrom/to standard unit (using area as an

example)

x10+24 x10+18 x10+12 x10+6 x10+4 x10+6 x10+12 x10+18 x10+24

pm

2

nm

2

m

2

mm

2

cm

2

m

2

km

2

Mm

2

Gm

2

Tm

2

x10-24 x10-18 x10-12 x10-6 x10-4 x10-6 x10-12 x10-18 x10-24

8/2/2019 NMMU ENG1 Section1A Rev2

11/13

8/2/2019 NMMU ENG1 Section1A Rev2

12/13

CONVERSION BETWEEN

CUBIC UNITS

Procedure for conversion of cubic valuefrom/to standard unit (using volume as an

example)

x10+36 x10+27 x10+18 x10+9 x10+6 x10+9 x10+18 x10+27 x10+36

pm3 nm3

m3 mm3 cm3 m3 km3 Mm3 Gm3 Tm3

x10-36 x10-27 x10-18 x10-9 x10-6 x10-9 x10-18 x10-27 x10-36

8/2/2019 NMMU ENG1 Section1A Rev2

13/13

EXAMPLE 3

Cubic units

Convert 6.4 cm3 to m3

Multiply by (10-2)3 or move decimal point

2x3 places to the left

6.4 cm3 = 6.4 x 10-6 m3 or 0.0000064 cm3

CONVERSION BETWEEN

CUBIC UNITS