The time constant of an `LR` circuit respresents the time in which the current in the circuit

Options

A. reaches a value equal to about `37%` of its final value
B. reaches a value equal to about `63%` of its final value
C. attains a constant value
D. attains `50%` of the constant value

Answer

B

Explanation

`i=i_(0)(1-e^(-t//tau))`
At `t=tau`
`i=i_(0)(1-e^(-tau//tau))`
`(i)/(i_(0))=1-e^(-1)=1-(1)/(e)=(e-1)/(e)`
`=(2.7-1)/(2.7)=(1.7)/(2.7)=0.63`