applied voltage appears across the resistor, the steady state has
been reached and ER is equal to E. The current is then at its
maximum value and is equal to E/R. Since the resistance of the
inductor is negligible, EL is equal to zero when the steady state is
reached.
Figure 17. RL circuit response to a step voltage
b. The voltage, current, and rate of current change during the
transient periods should be more closely examined to see how these
characteristics change with time. From the instantaneous current
Curve A in Figure 18, which is an enlargement of the first portion of
Figure 17C, it can be seen that the current starts from zero and
increases rapidly at first and then tapers off to practically a zero
rate of increase at the end of five time constants. (RL time
constants are discussed in Section II.) Since the
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