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RLC Series Circuit: At Large and Small Frequencies; Phasor Diagram
Response of an RLC circuit depends on the driving frequency—at large enough frequencies, inductive (capacitive) term dominates.
Learning Objective

Distinguish behavior of RLC series circuits as large and small frequencies
Key Points

RLC circuits can be described by the (generalized) Ohm's law. As for the phase, when a sinusoidal voltage is applied, the current lags the voltage by a 90º phase in a circuit with an inductor, while the current leads the voltage by 90∘ in a circuit with a capacitor.

At large enough frequencies
$(\nu \gg \frac{1}{\sqrt{2\pi LC}})$ , the circuit is almost equivalent to an AC circuit with just an inductor. Therefore, the rms current will be Vrms/XL, and the current lags the voltage by almost 90∘. 
At small enough frequencies
$(\nu \ll \frac{1}{\sqrt{2\pi LC}})$ , the circuit is almost equivalent to an AC circuit with just a capacitor. Therefore, the rms current will be given as V_{rms}/X_{C,} and the current leads the voltage by almost 90^{∘}.
Terms

rms
Root mean square: a statistical measure of the magnitude of a varying quantity.

Lenz's law
A law of electromagnetic induction that states that an electromotive force, induced in a conductor, is always in such a direction that the current produced would oppose the change that caused it; this law is a form of the law of conservation of energy.

resonance
The increase in the amplitude of an oscillation of a system under the influence of a periodic force whose frequency is close to that of the system's natural frequency.
Full Text
In previous Atoms we learned how an RLC series circuit, as shown in , responds to an AC voltage source. By combining Ohm's law (I_{rms}=V_{rms}/Z; I_{rms} and V_{rms} are rms current and voltage) and the expression for impedance Z, from:
we arrived at:
From the equation, we studied resonance conditions for the circuit. We also learned the phase relationships among the voltages across resistor, capacitor and inductor: when a sinusoidal voltage is applied, the current lags the voltage by a 90º phase in a circuit with an inductor, while the current leads the voltage by 90^{∘} in a circuit with a capacitor. Now, we will examine the system's response at limits of large and small frequencies.
At Large Frequencies
At large enough frequencies
At Small Frequencies
The impedance Z at small frequencies
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Key Term Reference
 AC
 Appears in this related concepts: Resistors in AC Circuits, Safety Precautions in the Household, and Impedance
 Law
 Appears in this related concepts: TwoComponent Forces, Physics and Other Fields, and Models, Theories, and Laws
 Ohm's law
 Appears in this related concepts: Energy Usage, Resistors in Parallel, and Ohm's Law
 atom
 Appears in this related concepts: Description of the Hydrogen Atom, Early Ideas about Atoms, and Periods 1 through 3
 capacitor
 Appears in this related concepts: Resistors and Capacitors in Series, ParallelPlate Capacitor, and ParallelPlate Capacitor
 circuit
 Appears in this related concepts: Combinations of Capacitors: Series and Parallel, Microwaves, and Maxwell's Equations
 current
 Appears in this related concepts: Reporting LongTerm Liabilities, The Battery, and Magnetic Force Between Two Parallel Conductors
 diagram
 Appears in this related concepts: Motion Diagrams, Power, and Bohr Orbits
 equation
 Appears in this related concepts: A General Approach, Equations and Inequalities, and Equations and Their Solutions
 frequency
 Appears in this related concepts: Wavelength, Freqency in Relation to Speed, Properties of Waves and Light, and Guidelines for Plotting Frequency Distributions
 impedance
 Appears in this related concept: Diffraction
 inductor
 Appears in this related concepts: Induced Charge, Energy Stored in a Magnetic Field, and RL Circuits
 ohm
 Appears in this related concepts: Poiseuille's Equation and Viscosity, Current and Voltage Measurements in Circuits, and Phase Angle and Power Factor
 phase
 Appears in this related concepts: The Kinetic Molecular Theory of Matter, The Phase of Orbitals, and The Production of Electromagnetic Waves
 phasor
 Appears in this related concepts: Resonance in RLC Circuits, Inductors in AC Circuits: Inductive Reactive and Phasor Diagrams, and Phasors
 resistor
 Appears in this related concepts: Charging a Battery: EMFs in Series and Parallel, The Loop Rule, and Introduction and Importance
 rms current
 Appears in this related concept: Capacitors in AC Circuits: Capacitive Reactance and Phasor Diagrams
 series
 Appears in this related concepts: Taylor Polynomials, Resisitors in Series, and Finding the General Term
 sinusoidal
 Appears in this related concepts: Driven Oscillations and Resonance, Sinusoidal Nature of Simple Harmonic Motion, and Root Mean Square Values
 voltage
 Appears in this related concepts: Conductors, Electric Potential Due to a Point Charge, and Principles of Electricity
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Source: Boundless. “RLC Series Circuit: At Large and Small Frequencies; Phasor Diagram.” Boundless Physics. Boundless, 03 Jul. 2014. Retrieved 15 Apr. 2015 from https://www.boundless.com/physics/textbooks/boundlessphysicstextbook/inductionaccircuitsandelectricaltechnologies22/accircuits162/rlcseriescircuitatlargeandsmallfrequenciesphasordiagram5826286/