Principles
Quantity, units and symbols
To avoid misunderstandings it is important to use the correct physical
expressions.
Physical
quantity
|
Symbol
|
SI
Unit
|
Symbol
|
Measurement
device
|
length
|
l
|
meter
|
m
|
ruler,
caliper
|
mass
or weight
|
m
|
gram
|
g
|
scale
|
pounds
|
lb
|
current
|
I
|
ampere
|
A
|
ammeter,
clamp meter
|
voltage
|
V
|
volt
|
V
|
voltmeter
|
resistance
|
R
|
ohm
|
Ω
|
ohmmeter
|
wattage,
power
|
P
|
watt
|
W
|
wattmeter
|
Examples: A current I is 2 A (Ampere).
The
voltage V is 12 V (Volt).
The
resistor R has 10 kΩ (kilo ohm). The resistor R13 in the circuit has
56 kΩ
(kilo ohm).
SI Prefixes
In practice the values of measurements are often too big or too small
to manage with the basic units only. The following prefixes are used in
electronics:
Prefix
|
Symbol
|
Factor
|
Power
of 10
|
giga
|
G
|
1 000 000,000
|
109
|
mega
|
M
|
1 000 000
|
106
|
kilo
|
k
|
1 000
|
103
|
|
milli
|
m
|
0.001
|
10-3
|
micro
|
µ
|
0.000 001
|
10-6
|
nano
|
n
|
0.000 000 001
|
10-9
|
pico
|
p
|
0.000 000 000 001
|
10-12
|
Examples: 1 A = 1 000 mA
100 kΩ = 100 000 Ω (or 0.1 MΩ)
97.6 MHz = 97 600 kHz (or 97 600 000 Hz)
100 nF = 0.1 µF (or 100 000 pF)
Usage
When converting a unit or a formula write down all steps carefully.
Do not do it mental! A 0 is lost and a . is put at a wrong place easily.
- Learn the sequences. For numbers which are bigger than the units: kilo – mega – giga
and for number smaller than the unit: milli – micro – nano – pico
- Remember that the steps between the following or the previous prefix is the
factor 1 000
- During converting the value remains the same. When the prefix gets bigger
(mega instead of kilo) the number must get smaller (1 instead of 1 000)
Examples: 1 A = ? mA
the difference of A to mA is 1 000
mA is smaller
than A. So the number must get bigger (x 1 000)
1 A = 1 000 mA
2.2 KΩ = ? Ω
the difference of KΩ to Ω is 1 000
Ω is smaller
than KΩ. So the number must get bigger (x 1 000)
2.2 KΩ = 2 200 Ω
3 000 V = ? kV
the difference of V to kV is 1 000
K is bigger than V. So the number must get smaller (/ 1 000)
3 000 V = 3 kV
94.5 MHz = ? Hz
the difference of M to the Hz is 1 000 000 (kilo is in between)
Hz is smaller than MHz. So the number must get bigger (x 1 000 000)
94.5 MHz = 94 500 000 Hz (or 94 500 kHz)
Exercises
Please convert the following values.
To see the answer just
the space in front of the target value.
1 000 V =
1 KV
1 000 mV =
1 V
2.2 KΩ =
2 200 Ω
3.3 MΩ =
3 300 KΩ
250 mV =
0.25 V
25 mV =
0.025 V
545 V =
0.545 KV
11 KV =
11 000 V
11 KV =
11 000 000 mV
500 µA =
0.5 mA
50 µA =
0.05 mA
50 µA =
0.000 05 A
0.230 KV =
230 V
220 nF =
0.22 µF
10 000 µF =
10 mF
10 000 µF =
10 000 000 nF
22 pF =
0.022 nF
Sources and additional information
SI-prefixes:
http://en.wikipedia.org/wiki/SI_prefix
Units:
http://en.wikipedia.org/wiki/Conversion_of_units
Unit converter:
www.cactus2000.de/uk/unit/mass.shtml