Current Flow is the flow rate
of electrons. One ampere of current is a flow rate of 6,250,000,000,000,000,000
electrons per second. As you can see, this is a very large number and the ampere
(amp) is a large unit of measure. We normally use the "milli" or even "micro"
multipliers to scale down this large unit.
There are two ways of referring to the flow of current:
Electron versus Conventional. Don't get this confused!
- Electron flow (technically correct) specifies
that current flows OUT of the NEGATIVE terminal of a power supply- through the
circuit- back to the POSITIVE power supply terminal. This is really what
happens. The negative terminal of a power supply has a SURPLUS of electrons,
and the POSITIVE terminal has an electron deficiency. When a power supply is
connected to a circuit, lost of "free" electrons flow from NEGATIVE power
supply terminal - through the circuit- back to the POSITIVE terminal
(electrons are attracted to the positively-charged atoms lacking electrons -
opposite charges attract).
- CONVENTIONAL current flow is the opposite to
that described above. POSITIVE - to - NEGATIVE flow. We will use CONVENTIONAL
current flow because it is the most popular model, and the solid-state
electronic symbols you will learn in ENT 178, 180, 281 all use arrows to
denote conventional flow direction.