Current
is Charge in Motion
Electrical conductors have
conduction electrons capable of moving in
response to electric force. Nonconductors
have charges that cannot move. The movement
of charges is defined as electric current.
Consider a wire with a cross section of
S with charges
moving through it. If in a period of time
 t,
q
coulombs cross S
in the direction of flow. Accordingly the
current will be
Mathematically, the relationship between
current i,
charge q,
and time t
can be written in differential form
Accordingly, the current
is the time rate of flow of charge and is
measured in amperes. dq
is the incremental value of charge crossing
a plane in an incremental time, dt.
Relationship Between Charge and
Current in Integral Form
The charge transferred
between time t0
and time t1
may be expressed as a definition integral
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