Basic Electrical Theory
METRIC SYSTEM AND POWERS OF TEN
TABLE A-3
DERIVED SI UNITS
Quantity
Derived
Symbol
Unit
Energy
joule
J
Force
newton
N
Power
watt
W
Electric charge
coulomb
C
Electric potential
volt
V
Electric resistance
ohm
W
Electric conductance
mho
Electric capacitance
farad
F
Electric inductance
henry
H
Frequency
hertz
Hz
Magnetic flux
weber
Wb
Magnetic flux density
tesla
T
Metric Prefixes
When working with basic electrical measurement units, sometimes the values are too large or too
small to express conveniently. For convenience, add metric prefixes (Table A-4) to the basic
unit. For example, if we have a resistor that is 1,000,000 ohms (W), we can add the prefix kilo,
or its designated symbol K, and express the value as 1,000 KW, or the metric prefix mega
(symbol M) and express the value as 1 MW. In the case of capacitance or current, we may have
a very small value such as 0.002 amperes (symbol A) or 0.000005 farads (symbol F). These
values can be expressed by adding the prefix milli (symbol m) and expressing the current as 2
milli amperes or 2 mA, or adding the prefix micro (symbol µ) and expressing the capacitance as
5 micro farads, or 5 µF.
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