**RLC parallel resonance circuit:**

Image by V4711 Attribution-Share Alike 3.0 Unported

- At
**low** frequencies, the inductor will have the **lower** impedance and will dominate the higher impedance of the C and the R. This means that most of the **current goes through the inductor**. As frequency **increases**, the impedance of L **increases** and current **decreases**.
- At
**high** frequencies, the capacitor will have the **lower** impedance and will dominate the higher impedance of the L and the R. This means that most of the **current goes through the capacitor**. As frequency **increases**, the impedance of C **decreases** and current **increases**.
- At resonance, the impedance of the L equals the impedance of C except they are 180 degrees out of phase with each other, cancel to create
**infinite**impedance and you are left with R as your impedance. This means that all of the** current goes through the resistor**.

Formula from: Parallel RLC Circuit and RLC Parallel Circuit Analysis

Here is impedance plotted versus frequency for a parallel RLC resonance.

Graphic from: Parallel Resonance and Parallel RLC Resonant Circuit

**RLC series resonance circuit:**

Image by V4711 CC BY-SA 3.0

- At
**low** frequencies, the capacitor will have the **higher** impedance and will dominate the **lower** impedance of the L and the R. This means that **the capacitor determines the amount of current flowing through the circuit.**As frequency **increases**, the impedance of C **decreases** and current **increases**.
- At
**high** frequencies, the inductor will have the **higher** impedance and will dominate the **lower** impedance of the C and the R. This means that **the inductor determines the amount of current flowing through the circuit. **As frequency **increases**, the impedance of L **increases** and current **decreases**.
- At resonance, the impedance of the L equals the impedance of C only they are 180 degrees out of phase with each other, cancel to create
**zero**impedance and you are left with R as your impedance.

Formula from: Series RLC Circuit and RLC Series Circuit Analysis

Here is impedance plotted versus frequency for a series RLC resonance (ignore the weird kink at higher frequencies.).

Graphic from Series Resonance in a Series RLC Resonant Circuit

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### Stephen L. Martin

Attempting to balance a materialist, atheist and secular worldview of my thoughts with the openness of a Buddhist heart; retired electrical engineer; certified NLP Practitioner; intensive psychotherapy work; composer and guitar player.
View all posts by Stephen L. Martin