(Solved): 7.1 The switch in the circuit of Fig. P7.1 has been closed for a long time and opens at t = 0. a. ...

7.1 The switch in the circuit of Fig. P7.1 has been closed for a long time and opens at t = 0.
a. Calculate the initial value of i.
b. Calculate the initial energy stored in the inductor.
c. What is the time constant of the circuit for t > 0?
d. What is the numerical expression for i(t) for t? 0
?
?
?
e. What percentage of the initial energy stored has been dissipated in the resistor 202 5 ms after the
switch opens?
Answers (a) Io = -12.5A, (h) w(0) = 625mJ, (c) t = 4ms, (d) i(t) =
-12.5e-250t A, t? 0, (e)%w(5ms) = 91.8%
t = 0
120 V
+
3 ?
6?
?30 ?
8 mH 20

7.1The switch in the circuit of Fig. P7.1 has been closed for a long time and opens at $t=0$. - a. Calculate the initial value of $i$. - b. Calculate the initial energy stored in the inductor. - c. What is the time constant of the circuit for $t>0$ ? - d. What is the numerical expression for $i(t)$ for $t?0$ e. What percentage of the initial energy stored has been dissipated in the resistor $2?5\mathrm{ms}$ after the switch opens? Answers (a) $I_o=?12.5A,(b)w(0)=625\mathrm{m}J$, (c) $?=4ms,(d)i(t)=$ $?12.5e^{?250t}A,t?0,(e)\%w(5ms)=91.8\%$