Solve the Problem $\mathrm { L } \frac { \mathrm { di } } { \mathrm { dt } } + \mathrm { Ri } = 0$

Multiple Choice

Solve the problem.
-If the switch is thrown open after the current in an RL circuit has built up to its steady-state value, the decaying current obeys the equation $\mathrm { L } \frac { \mathrm { di } } { \mathrm { dt } } + \mathrm { Ri } = 0$ . How long after the switch is thrown open will it take the current to fall to $35 \%$ of its original value?

A) -4.60 L/R seconds
B) -4.40 L/R seconds
C) 1.25 L/R seconds
D) 1.05 L/R seconds