(c) During the third constant, current again increases:

10 amperes 8.64 amperes = 1.36 amperes

1.36 amperes x .632 = 0.860 ampere

8.64 amperes + 0.860 ampere = 9.50 amperes

(d) During the fourth time constant, current again

increases:

10 amperes 9.50 amperes = 0.5 ampere

0.5 ampere x .632 = 0.316 ampere

9.50 amperes + 0.316 ampere = 9.82 amperes

(e) During the fifth time constant, current increases as

before:

10 amperes 9.82 amperes = 0.18 ampere

0.18 ampere x .632 = 0.114 ampere

9.82 amperes + .114 ampere = 9.93 amperes

Thus, the current at the end of the fifth time constant is

almost equal to 10.0 amperes, the maximum current. For all

practical purposes, the slight difference in value can be

ignored.

(2) *Deenergization of an LR Circuit*. When an LR circuit is

deenergized, the circuit decreases (decays) to zero in five time

constants at the same rate that it previously increased. If the

growth and decay of current in an LR circuit are plotted on a

graph, the curve appears as shown in figure 21 on the previous

page. Notice that the current increases and decays at the same

rate in five time constants.

The value of the time constant in seconds is equal to the

inductance in Henrys divided by the circuit resistance in Ohms.

The formula used to calculate one L time constant is:

R

L (in Henrys)

t (in seconds) =

R (in Ohms)

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