Question

In an `LR`-circuit, time constant is that time in which current grows from zero to the value (where `I_(0)` is the steady state current)
A. `0.63I_(0)`
B. `0.50I_(0)`
C. `0.37I_(0)`
D. `I_(0)`

Answer 1

Correct Answer - A
Current at any instant of time `t` after closing an `L-R` circuitis given by `I=I_(0)[I-e^(-(R )/(L)t)]`
Time cionstant `t=(L)/(R )`
`:.I=I_(0)[i_(0)-e^((-R)/(L)xx(L)/(R ))]=I_(0)(1-e^(-1))=I_(0)(1-(1)/(e))`
`=I_(0)(1-(1)/(2.718))=0.63I_(0)=63%ofI_(0)`