Electric Current
The number of electrons flowing past a single point per second is
referred to as electric current. The SI unit for current is the ampere
(A). We measure electric current with an ammeter.
quantity of charge
change in time
Q
I=
Δt
current =
When a current of 1A flows through a conductor for 1s, 1C of charge
passes any point in the conductor. 1C of charge is equal to
6.24 ×1018 electrons.
Question: A typical lightning flash lasts a quarter of a second and the
peak current is about 15kA. Determine the quantity of charge in
coulombs transferred by this lightning strike. Approximately how
many electrons is this?
How fast do
electrons flow?
What does this say
about electrons?
WHICH WAY DO ELECTRONS FLOW? DO WE KNOW?
2 THEORIES
Conventional Current
Today, the term current (I) means the flow of positive charge from the
anode to cathode in a circuit. (positive terminal to negative terminal)
This was the convention chosen during the discovery of electricity.
Electron Flow
The flow of negative charge from cathode to anode is called electron
flow. (negative to positive terminal)
Both Conventional Current and Electron Flow are used by industry. In
fact, it makes no difference which way current is flowing as long as it
is used consistently. The direction of current flow does not affect what
the current does.
We will use the conventional current theory since a wealth of theory
was based on this convention.