, between times t
and (t + Dt)] 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