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Homework Help: The current in RLC circuit.

  1. Feb 12, 2017 #1
    1. The problem statement, all variables and given/known data
    In the tuned circuit below, what will happen to the reading of the ammeter when:
    a) source frequency increases. The voltage is constant
    b) the capacitance increases. The voltage and source frequency are constant
    c) The voltage increases. Source frequency is constant.

    2. Relevant equations
    ƒ =1/(2π√LC) Where: C is the capacitance and L is the inductance.
    I= V/Z Where: V is the voltage and Z is the impedance.

    3. The attempt at a solution
    Here is my solution:

    a) the ammeter reading decreses.
    Explanation: when source frequency varies the circuit is no longer in resonance so the impedance increases,
    Z=√R²+ (Xl-Xc)²

    b) the ammeter reading decreases.
    Explanation: when the capacitance C increases, Xc decrease, then (Xl-Xc) increses, hence the impedance increases because:
    Z= √R²+(Xl-Xc)²

    c) the ammeter reading increases.
    Explanation: since source frequency is constant, the circuit is still in resonance. So, increasing in voltage will increase the current becuase the impedance of the circuit will not change.

    Am I correct?
  2. jcsd
  3. Feb 12, 2017 #2


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    Homework Helper

    Yes, it is correct. Well done!
  4. Feb 12, 2017 #3
    Thank you, ehild!
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