needs solution

Discussion in 'Math' started by shaider530, Jul 9, 2007.

  1. shaider530

    Thread Starter New Member

    Jul 7, 2007
    6
    0
    4i + 8 int idt - 3 di/dt = 50 cos(2t +75 degrees)
    find the current?
     
  2. shaider530

    Thread Starter New Member

    Jul 7, 2007
    6
    0
    4i + 8\int idt - 3 di/dt = 50 cos(2t +75 degrees)
    find the current.
     
  3. recca02

    Senior Member

    Apr 2, 2007
    1,211
    0
    are you familiar with laplace transform?
     
  4. shaider530

    Thread Starter New Member

    Jul 7, 2007
    6
    0
    no im not familiar with laplace transform. what is that?
     
  5. recca02

    Senior Member

    Apr 2, 2007
    1,211
    0
    laplace transform is very useful for finding various parameters and solutions to complex circuits and equations.
    u can get some idea abt it from here.
    http://en.wikipedia.org/wiki/Laplace_Transform
    u may for now have to solve the above equation using solution methods for differential equations.
     
  6. omnispace

    Member

    Jul 25, 2007
    27
    0
    I think this is easiest with phasors...

    4*I + (8*I)/(j*w) - 3*j*w*I = 50<75
    w = omega = 2
    4*I - (j*8*I)/2 - j*6*I = 50<75
    add the imaginary terms
    4*I - j*65*I = 50<75
    convert to polar form
    65.123<-86.5 * I = 50<75
    divide the magnitudes and subtract the angles
    I = 0.7678<161.5
    i = 0.7678*cos(2t + 161.5 degrees) A

    This is very similar to the Laplace transform...basically "s" becomes "jw", like Fourier. But w is constant, so it is in "phase-domain" instead of frequency-domain.

    You might want to double-check my algebra/arithmetic, I'm not really that awake.
     
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