Trying to understand graph from simple LC circuit

Discussion in 'Homework Help' started by andy24691, Dec 9, 2010.

  1. andy24691

    Thread Starter Member

    Nov 25, 2010
    42
    0
    If you had a circuit consisting of a voltage source in parallel with a resistor which is in parallel with an inductor, the relationship between the voltage input and the total current looks like this.

    [​IMG]

    Why does it look like this?
    Also with true power up the y-axis instead of current the graph is almost identical in shape. Why is this?

    I've looked into the maths and I can't explain why the graphs look like this, I'm sure its quite simple but I can't seem to get my head around it.

    cheers
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    63
    Post the circuit.
     
  3. andy24691

    Thread Starter Member

    Nov 25, 2010
    42
    0
    Its just a voltage source connected to a resistor and inductor in parallel.[​IMG]
     
  4. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    A DC voltage source?
     
  5. andy24691

    Thread Starter Member

    Nov 25, 2010
    42
    0
    Its a AC source.
     
  6. tyblu

    Member

    Nov 29, 2010
    199
    16
    Z_{eff.} = R || sL = \frac{sLR}{R + sL} = \frac{sLR}{R + sL} \cdot \frac{1/sL}{1/sL}<br />
 = \frac{R}{1+ \frac{R}{sL}} \\<br />
i_{source} = v_{source}/Z_{eff.}<br />
 = v_{source} \cdot \frac{1 + \frac{R}{sL}}{R}<br />
 = \frac{v_{source}}{R} (1 + \frac{R}{sL})<br />

    Is this what you get? This follows Ohm's law, not the given graph.
     
  7. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    What is the frequency, the inductance and the resistance?

    How did you get that graph?
     
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