Volts is electrical pressure  the potential difference measured between 2 points in a circuit
Amps is electrical current  the 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 Oscilloscopes (CRO)

Multiples and submultiples 
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. 
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: 
Question: 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 
Question: 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
Example
Scientific Notation
mega
M
1,000,000
107MHz = 107,000,000 hertz
106
kilo
k
1000
5kV = 5000 volts
103
milli
m
0.001
6mA = 0.006 amps
103
micro
u
0.000001
2uA = 0.000002 amps
106

Conversion Examples: 
Question: 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 


Question: 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) 
