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Quick question on Parallel RLC circuit (Conceptual)

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Homework Statement


Even conceptual problem in the text:

Consider a standard RLC circuit driven by an AC source in which the elements are in parallel. Construct a phasor diagram and develop an expression for the phase angle θ. Now remove the resistor from the circuit, can you still develop an expression for the phase angle? Why or why not?


The Attempt at a Solution



The first part I was able to do with ease.

If we remove the resistor, then in my diagram I have the current through the capacitor (which lies on the vertical axis, and points upward), the current through the inductor (which lies on the vertical axis, and points downward), and the source voltage ( which lies on the horizontal axis, and points to the right). If we remove the resistor, I argue that the max current will strictly be pointing along the vertical axis and therefore the phase angle will be 0 radians. In addition, if I look at the expression I developed for the phase angle in an RLC circuit in parallel, if I allow R = 0, I again see that the phase angle is necessarily zero.

Am I correct?

Edit - I suppose my question is, when I say phase angle, am I talking about the angle with respect to the voltage? Because if that is the case then my angle is 90 degrees.
 
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Answers and Replies

  • #2
cnh1995
Homework Helper
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Homework Statement


Even conceptual problem in the text:

Consider a standard RLC circuit driven by an AC source in which the elements are in parallel. Construct a phasor diagram and develop an expression for the phase angle θ. Now remove the resistor from the circuit, can you still develop an expression for the phase angle? Why or why not?


The Attempt at a Solution



The first part I was able to do with ease.

If we remove the resistor, then in my diagram I have the current through the capacitor (which lies on the vertical axis, and points upward), the current through the inductor (which lies on the vertical axis, and points downward), and the source voltage ( which lies on the horizontal axis, and points to the right). If we remove the resistor, I argue that the max current will strictly be pointing along the vertical axis and therefore the phase angle will be 0 radians. In addition, if I look at the expression I developed for the phase angle in an RLC circuit in parallel, if I allow R = 0, I again see that the phase angle is necessarily zero.

Am I correct?

Edit - I suppose my question is, when I say phase angle, am I talking about the angle with respect to the voltage? Because if that is the case then my angle is 90 degrees.
Seems right. Removing the resistor will make the circuit purely reactive. Wheather its leading or lagging will be decided by L and C values.
 

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