Understanding Phase Change: R, L & C

In summary, considering phase change is necessary because complex impedances can cause a phase shift between voltage and current, which is important to understand for solving complex impedance problems. This can be seen in the example of an inductor, where the current lags behind the voltage, resulting in a phase shift between the two.
  • #1
hidemi
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Homework Statement
If the input to an RLC series circuit is V = Vm Cos ωt, then the current in the circuit is?
The answer is (D) as attached.
Relevant Equations
V = IZ
Z = [ R^2 + (XL - Xc)^2]^1/2
Why do we need to consider phase change?
Here are my thoughts: is it because voltages are different in phase for each of the three electrical accessories, R, L and C?
 

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  • #2
Because complex impedances will, in general, cause a phase shift between the voltage applied and the current. It's what they do. Suppose Z is just an inductor, would the current be in phase with the voltage?
 
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  • #4
DaveE said:
Because complex impedances will, in general, cause a phase shift between the voltage applied and the current. It's what they do. Suppose Z is just an inductor, would the current be in phase with the voltage?
No, the current will be lagged after voltage.
 
  • #5
hidemi said:
No, the current will be lagged after voltage.
Which will appear as a phase shift between the voltage and current. That is why phase matters for complex impedance problems.
 
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  • #6
DaveE said:
Which will appear as a phase shift between the voltage and current. That is why phase matters for complex impedance problems.
Thank you for your further explanation.
 

FAQ: Understanding Phase Change: R, L & C

What is phase change in terms of R, L & C?

Phase change refers to the change in the relationship between voltage and current in a circuit when the values of resistance (R), inductance (L), or capacitance (C) are altered. This change can be seen in the phase angle, which is the difference in phase between voltage and current.

How do R, L & C affect phase change?

Resistance (R) affects phase change by causing a voltage drop and shifting the phase angle. Inductance (L) causes a phase shift between current and voltage due to the buildup of a magnetic field. Capacitance (C) also causes a phase shift, but in the opposite direction, due to the buildup of an electric field.

What is the relationship between phase change and frequency?

The relationship between phase change and frequency is inverse. As frequency increases, the phase angle decreases, and vice versa. This is because at higher frequencies, the reactance of inductors and capacitors becomes more significant, causing a greater phase shift.

How does phase change affect power in a circuit?

Phase change can affect power in a circuit by causing a difference in the power factor. A power factor of 1 indicates that the voltage and current are in phase, and the circuit is using all the available power. A lower power factor, caused by a phase shift, means that some power is being lost in the circuit.

How can phase change be measured and controlled?

Phase change can be measured using an oscilloscope, which can display the phase difference between voltage and current. It can also be controlled by adjusting the values of R, L, and C in a circuit. This can be done manually or through the use of devices such as variable resistors, inductors, and capacitors.

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