## Question File Number 04

### Measurement Units

The units for voltage, current, resistance and power are covered in other parts of this Study Guide. Go to:  Voltage    Current   Resistance  and Power

You must become familiar with the smaller and larger units often used in radio work. For example, be sure that you know the relationships between (and can convert) (say) millivolt to volt, volt to kilovolt, microamp to a milliamp, megohms to ohms, kilo-ohms to ohms, watt to milliwatt, etc. The following table will be useful.

### Scientific Notation

T

tera

x 1 000 000 000 000

1012

G

giga

x 1 000 000 000

109

M

mega

x 1 000 000

106

k

kilo

x 1 000

103

m

milli

÷ 1 000

10-3

u

micro

÷ 1 000 000

10-6

n

nano

÷ 1 000 000 000

10-9

p

pico

÷ 1 000 000 000 000

10-12

f

femto

÷ 1 000 000 000 000 000

10-15

a

alto

÷ 1 000 000 000 000 000 000

10-18

### Impedance

The ohm is the unit for resistance. It is also the unit for impedance. What is impedance?

The capacitor and the inductor each exhibit reactance. See Capacitors and Inductors

As first concept, reactance can be broadly viewed as an AC resistance equivalent for capacitors and for inductors. This is only satisfactory as a first approach to the subject.

Impedance is a combination of both resistance and reactance. The term impedance implies that RF circuitry is involved, with either discrete components or with transmission lines. Transmission Lines

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Compiled Mon Nov 29 2010 at 8:11:49pm

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