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Homework Help: When Voltage is Constant (DC), is current also constant?

  1. Oct 27, 2016 #1
    1. The problem statement, all variables and given/known data

    When Voltage is oscillating (A/C), then in a simple circle with steady resistance, the current will be proportional to the voltage. When voltage increases, current will increase. And when voltage decreases, voltage will decrease. Is it also true that in a simple circuit with constant resistance, when voltage is steady (DC), then current will also be steady.

    by "steady," I mean a horizontal line on the graph.

    2. Relevant equations

    V = IR

    3. The attempt at a solution
    Supposing this is correct based on observing that graphs of AC voltage (represented by some sort of sine function) are usually accompanied by current represented by a sine function. I have not seen an a/c voltage graph accompanied by a steady horizontal line for current.

    Thus I assume that if current is to remain proportional to a steady resistance, the current has to maintain the same "flow pattern" (perhaps different amplitude, but same frequency and phase etc) on the graph as voltage.

  2. jcsd
  3. Oct 27, 2016 #2
    That is true when the circuit contains pure resistance. To the extent the circuit possesses inductance or capacitance, however, voltage and current will be out of phase.
  4. Oct 27, 2016 #3


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    Homework Helper
    Gold Member

    If the circuit contains only resistors, then the current will be constant.
    If the circuit contains energy storing elements like inductor or capacitor, the transient of the current is a combination of exponential and sinusoidal function w.r.t time.
    Look up 'step response of series RLC circuit.'
  5. Oct 27, 2016 #4
    Thank you both.
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