1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: I would like to verify these answers please

  1. Apr 11, 2008 #1
    I would like to verify these answers please..

    What is the inductance of a series RL circuit in which R=1.0 K ohms if the current increases to 1/3 of it's final value in 30 Ms (M is the greek symbol Mu).

    Is the answer 30 (none of these) or is it 74mH?? I calculated 74mH

    i(t) = I (1-1/e^t/τ)

    given i(t) = 1/3*I and t =30uS and τ =L/R

    so,,substitutin these values

    we get t/τ = 0.41

    30*10^-6 / τ = 0.41

    τ ˜ 74 μ sec

    L/R ˜ 74usec

    R = 1K

    so,,L ˜74mH

    The choices for answers are.

    1.) 49
    2.) none of these
    3.) 99
    5.) 62

    Last edited: Apr 11, 2008
  2. jcsd
  3. Apr 12, 2008 #2

    Tom Mattson

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I get 74mH too.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook