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How to Calculate Resonance in an LRC

An LRC filter is a circuit used in televisions, radios and other electronic devices that selects a narrow band of frequencies from a complex input signal. The "LRC" comes from the symbol "L" for electrical inductance, "R" for resistance and "C" for capacitance. A capacitor, inductor and resistor, connected in a series circuit, form an LRC filter. It has a band-pass response, meaning it has a single resonant, or preferred, frequency, and it progressively rejects lower and higher frequencies. An LRC filter can therefore tune in a particular station on a radio.

Things You'll Need

Scientific calculator

Instructions

- 1
  Key the LRC circuit's inductor value in henrys into the calculator. Use scientific notation, if necessary. For example, the circuit has an inductor of 10 microhenrys, or 1 * 10^-5 henrys. Press the multiply key.
- 2
  Enter the circuit's capacitance value in farads. Again, use scientific notation. Following the example, a .02 microfarad capacitor is .02 * 10^-6 or 2 * 10^-8 farads. Press the equals key to see 2 * 10^-13. Press the square root key and see 4.472 * 10^-7.
- 3
  Press the "1/x" key to obtain the reciprocal of the previous result. In this example, pressing 1/x gives 2.236 * 10^6, or 2,236,000. This is the resonant frequency of the LRC circuit in hertz, or cycles per second.

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