Turtleand Energy

Rung 9 · See fields and systems

Find series resonance

Sweep an RLC circuit around 50 Hz and watch current peak when energy exchange lines up.

intermediate40 minutes0 of 4 stages explored
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A five volt alternating source feeding a resistor, inductor, and capacitor in one series loop.
5 V AC source -> 100 ohm resistor -> 100 millihenry inductor -> 100 microfarad capacitor -> return

Knowledge this exercise builds on

Lesson 5: DC vs ACLesson 9: Generators and Electromagnetic Induction

Practice loop

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ComponentsSee the parts and values before you start.
  • One adjustable 5 V peak AC voltage source
  • One 100 Ω resistor
  • One 100 mH inductor
  • One 100 µF capacitor
  • Voltage and current scopes
PredictCommit to an expected result before running the circuit.

Estimate the resonant frequency with:

f₀ = 1 / (2π√LC)

Predict how current at 20 Hz and 100 Hz will compare with current near 50 Hz.

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For 100 mH and 100 µF:

f₀ ≈ 50.3 Hz

Current should be highest near 50 Hz and lower at 20 Hz and 100 Hz. Below resonance, current leads source voltage. Above resonance, current lags it.

BuildWire the circuit yourself from a blank canvas.

Place the resistor, inductor, and capacitor in one series loop. Start the source at 20 Hz, then test 50 Hz and 100 Hz.

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Use one unbranched path:

AC source -> 100 Ω -> 100 mH -> 100 µF -> source return

Keep component values fixed and change only source frequency. Scope source voltage and loop current.

MeasureSee what to inspect, compare, and change.

Measure current amplitude and its timing relative to source voltage at 20 Hz, 50 Hz, and 100 Hz.

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Current reaches its maximum near 50 Hz, where the inductor and capacitor reactances nearly cancel. At 20 Hz the circuit is net capacitive, so current leads source voltage. At 100 Hz it is net inductive, so current lags. Resistance limits the resonance peak.

ExplainConnect the observation back to your model.

Explain how the capacitor’s electric field and inductor’s magnetic field exchange energy, and how the resistor damps that exchange.

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Near resonance, energy moves back and forth between the capacitor’s electric field and the inductor’s magnetic field. The resistor converts some of that energy to heat every cycle, which damps the exchange. Resonance is frequency-selective behavior, not free energy. The source replaces the energy dissipated by resistance.

Optional referenceReveal reference circuitCompare only after you build. Opening this panel does not contact Falstad.

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Safety boundary

This is a low-voltage educational model.

Do not translate it into mains construction, household wiring, battery-pack work, or real protection settings. Real electrical systems need rated components, proper protection, test equipment, and qualified safety judgment.