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In Fig. the switch is closed and steady-state conditions are established. The switch is thrown open at t = 0. a. Find the initial voltage E_(0) across L just after t = 0. Which end of the coil is at the heigher potential : a or b? b. Makefreehand graphs of the current in R_(1) and R_(2) as a funtion of time, treating the steady-state directions as positive. Show values before and after t = 0. c. How long after t = 0 does the current in R_(2) have the value 2 mA? |
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Answer» SOLUTION :a. `b` shell be at a higher potential `E_(0) = I_(0)(R_(1) + R_(2)) = 9 xx 8 = 72 V` b. `I = I_(0)e^(-((R_(1)+R_(2))t)/(L))`for `t = gt 0` `I` through `R_(1)`  `I` through `R_(2)`  c. `I = 9 e^((-8t)/(0.4))` `2 xx 10^(-3) = 9 e^(-20t) rArr e^(20t) = (9 xx 10^(3))/(2)` `20t = In (4.5 xx 10^(3))` `t = (1)/(20) In (4.5 xx 10^(3))s` |
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