1. Not finding help here? Sign up for a free 30min 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!

Inductance and RL circuits help

  1. Oct 30, 2009 #1
    If the switch is closed at t = 0, find the
    current in the inductor at t = 0.224 s. Answer
    in units of A.
    &
    Find the current in the switch at that same
    time.

    I know that i must use i = V/R(1 - e^-t/L/R) but cant seem to get the right answer.

    Any help is appreciated


    ................5 ohms
    -------------^^^^^^^------I
    I........................................I
    I.......10 ohms............1.4 H...I
    I------^^^^^^^^---&&&&--I
    I........................................I
    I.......S.........30 V.....5 ohms.I
    I-------/..---I I----^^^^^--I
    1. The problem statement, all variables and given/known data

    What am I doing wrong?

    2. Relevant equations

    i = V/R(1 - e^-t/L/R)

    3. The attempt at a solution

    i = V/R(1 - e^-t/L/R + V/5 = (30 - V)/5

    (V/10)( 1 - e^-(0.224*10/1.4) + V/5 = -V/5 + 6

    0.1V(0.798)+0.4V = 6

    (0.4+0.0798)V = 6

    V = 6/0.4798 = 12.5 v

    The inductor current at t = 0.224 s

    i = V/R(1 - e^-t/L/R)

    i = (12.5/10)[ 1 - e^-(0.224(10/1.4) ]

    i = 0.9976 A

    The switch current:

    Is = i + V/5 = 0.9976 + 12.5/5 = 3.497 A
     
    Last edited: Oct 30, 2009
  2. jcsd
  3. Oct 30, 2009 #2

    rl.bhat

    User Avatar
    Homework Helper

    First of all you have to find the voltage across LR circuit.
    At t=0 L acts like a conductor. Find the total resistance and current in the circuit. Hence find the voltage across LR circuit.Then use relevant formula to find the current in L.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Inductance and RL circuits help
  1. Inductance RL Circuit (Replies: 3)

  2. Inductance, RL Circuits (Replies: 13)

Loading...