In an $L-R$ circuit,the current reaches $\frac{3}{4}$ of its maximum value in $4 \ s$. What is the time constant of the $L-R$ circuit?

  • A
    $\frac{1}{\ln 2} \ s$
  • B
    $\frac{2}{\ln 2} \ s$
  • C
    $\frac{3}{\ln 2} \ s$
  • D
    $\frac{4}{\ln 2} \ s$

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