The four basic units of electrical measurement
are Volts, Amps, Ohms and Watts. 
Volts is
electrical pressure  the potential difference measured between 2
points in a circuit 
Amps is
electrical current  the (conventional) flow of current in a circuit
from positive to negative 
Ohms is
electrical resistance  the opposition to current flow in a circuit 

Watts is electrical power  the electrical
energy in a circuit 
Click here to
see Ohms law using Volts, Amps, Ohms and Watts 
To measure electrical units we need to use an instrument
called a meter. 
Meters come in all shapes and sizes,
each for a different purpose. We can have special purpose meters that
measure just one type of unit such as watts or an instrument called
a multimeter which is capable of measuring volts, amps and ohms. 
Even though the multimeter
can measure three electrical units, the meter must be connected differently
in the circuit. 
To measure Volts  connect the
meter in parallel with the circuit under measurement while
connected to the supply. 
To measure Amps  connect the
meter in series with the circuit under measurement while
connected to the supply. 
To measure Ohms  connect the
meter in parallel with the circuit under measurement with
the supply disconnected. 
Click
here to learn more about meters Click
here to learn more about Cathode Ray Oscilloscopes (CRO) 

Multiples and submultiples


Electrical measurements can be from thousands of
amps to millionths of an amp.

Terms used for these measurements 'kilo' and 'milli'
are called multiples and submultiples.

A few examples are listed in the following table:

Term

Symbol

Multiplier

Example

mega

M

1,000,000

107MHz = 107,000,000 hertz

kilo

k

1000

5kV = 5000 volts

milli

m

0.001

6mA = 0.006 amps

micro

u

0.000001

2uA = 0.000002 amps


Conversion Examples

1. A resistance reading is 4.7 Megohms. How
many ohms does this represent?

Answer:

Mega is one million so multiply 4.7 by 1,000,000
by moving the decimal point six places to the right 4,700,000
ohms

2. There is 2.45 mA flowing in a circuit.
How many amps is this?

Answer:

Milli is one thousand so divide 2.45 by 1,000 by
moving the decimal point 3 places to the left 0.00245 amps


Scientific Notation 
Scientific Notation is a way
of expressing multipliers (see previous table) in mathematical form.
Each multiplier is treated as a power of 10. Following are examples
scientific notation using the examples from the previous table: 
Term

Symbol

Multiplier

Scientific Notation 
Example

mega

M

1,000,000

106 
107MHz = 107,000,000 hertz

kilo

k

1000

103 
5kV = 5000 volts

milli

m

0.001

103 
6mA = 0.006 amps

micro

u

0.000001

106 
2uA = 0.000002 amps


Conversion Examples 
1. Convert 10kV to volts 
Answer: 
10kV

=

10 x 103 V

(k = 103) 

=

100 x 102 V

(1 decimal place right) 

=

1000 x 101 V

(2 decimal places right) 

=

10000 x 100
V

(3 decimal places to right) 
10kV

=

10,000 V



2. Convert 0.10mA
to microamps (uA) 
Answer: 
0.10mA

=

0.10 x 103
A

(m = 103) 

=

1.0 x 104 A

(1 decimal place right) 

=

10 x 105 A

(2 decimal places right) 

=

100 x 106 A

(3 decimal places to right) 
0.10mA

=

100 uA

(u = 106) 
