Then, the current at time t across the cross-section of the
conductor is defined as the value of the ratio of DQ to Dt in the limit of Dt
tending to zero,
( )
lim0
t
Q
I t
t
∆ →
∆
≡
∆
(3 2)
In SI units, the unit of current is ampere An ampere is defined
through magnetic effects of currents that we will study in the following
chapter An ampere is typically the order of magnitude of currents in
domestic appliances