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v R1<br />

R1 Defined<br />

polarity<br />

+<br />

vL –<br />

v L :<br />

Defined<br />

polarity Switch<br />

closed<br />

Defined<br />

direction<br />

+<br />

v R2<br />

–<br />

i L<br />

+ –<br />

Defined<br />

polarity<br />

R 2<br />

E<br />

0<br />

–125<br />

i L :<br />

v R1 :<br />

v R2 :<br />

25<br />

0<br />

50<br />

0<br />

50<br />

0<br />

75<br />

50 V<br />

5t<br />

5(2 ms)<br />

= 10 ms<br />

(mA)<br />

volts<br />

volts<br />

5t<br />

5t<br />

5t<br />

Switch opened<br />

5t′ = 5(0.8 ms) = 4 ms<br />

5t′<br />

5t′<br />

5t′<br />

Instantaneous<br />

change<br />

No instantaneous<br />

change<br />

Same shape<br />

as i L since<br />

v R1 = i L R 1<br />

FIG. 12.30<br />

The various voltages and the current for the network of Fig. 12.29.<br />

a calculator or table to determine the magnitude of the exponential<br />

term.<br />

The similarity between the equations v C � E(1 � e �t/t ) and i L �<br />

I m(1 � e �t/t ) results in a derivation of the following for t that is identical<br />

to that used to obtain Eq. (10.24):<br />

t � t loge�� Im<br />

�<br />

Im � i � L<br />

t<br />

t<br />

t<br />

t<br />

(12.21)<br />

INSTANTANEOUS VALUES ⏐⏐⏐ 491

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