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Homework Help: Voltage, Current, and Time Graph with Sine Wave

  1. Apr 2, 2013 #1
    1. The problem statement, all variables and given/known data

    Hello all! Basically, my professor used this graph in our lecture, but I do not really understand how to read it. The graph has three variables, so I'm guessing it is Voltage vs. Current as time increases? One question he asked was "The figure shows the voltage and current for a device. The frequency of the voltage is___" with the correct answer being 2.5 Hz.

    2. Relevant equations

    This graph makes very little sense to me, but I know that ω=2∏f
    Would the self-inductance formula work here? ε=-L(ΔI/Δt)
    This is the only equation I can think of that includes Volts, Amperes, and seconds.

    3. The attempt at a solution

    I know the sine waves are in phase with different amplitudes, but the arrows pointing in opposite directions must mean something? Should I choose the point where both the emf and the current are zero?

    Attached Files:

    Last edited: Apr 2, 2013
  2. jcsd
  3. Apr 2, 2013 #2


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    I think the arrows are just showing you which axis/scale applies to each graph. ie peak voltage is 2, peak current is 0.3 [I forgot to check whether they were Volts/millivolts and amps/milliamps etc.

    This could be the voltage vs current values for a standard ohmic component. To find the resistance of that component you choose any point on the graph and apply R = V/I choosing a point where both V and I are 0 wouldn't help refine your answer - I would choose the peak positions.
  4. Apr 2, 2013 #3


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    If you were only after the frequency, the graph shows the Period (time for a full cycle) is 0.4 seconds. That gives a frequency of 2.5 f = 1/T
  5. Apr 2, 2013 #4
    yeah choose the point where both emf and the current are zero
    Last edited: Apr 2, 2013
  6. Apr 2, 2013 #5
    Oh that makes so much sense! How simple! Thank you so much for breaking all of this down. So in a way I can look at this like two separate graphs/break it into components? And I guess the maximum values make more sense than using zero for other questions relating to this.

    Thanks a bunch!
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