calculating inductor voltage and current

Discussion in 'Homework Help' started by markp912, Feb 23, 2009.

  1. markp912

    Thread Starter Member

    Feb 4, 2009
    In problem 21(see attached image) i need to find the inductor voltage at a certain time. I tried using V=L(di/dt) but i dont think that formula is correct.

    Then on problem 22 i am totally confused on. Current equals i=v/r. but what am i given the times for then?

    Thank you in advance for your help!
  2. vvkannan

    Active Member

    Aug 9, 2008
    Hi markp912,
    For question no 21) the voltage across the inductor is given by VL =V(exp(-t/tau)
    where V is the dc supply

    and tau ->time constant = L/R
    iinitially the inductor would have 15 volts
    (since it acts as OPEN CIRCUIT)

    at steady state VL = 0 (since it acts as short circuit)

    Inbetween the voltage decreases exponentially

    see this page for further explanation
  3. markp912

    Thread Starter Member

    Feb 4, 2009
    thank you for your help. i got it.