Resonance in a series RLC circuit

Tune a circuit like a musical note

RLC means Resistor Inductor Capacitor: a resistor dissipates energy, a coil stores magnetic energy, and a capacitor stores electric energy. Resonance is the frequency where their opposing reactances cancel; reactance is opposition to a changing current. mH is millihenry, one thousandth of a henry of inductance; nF is nanofarad, one billionth of a farad of capacitance. Hz counts cycles per second.

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EXPERIMENT BENCH

Change the circuit settings, predict the readings, then check a challenge. These are learning models, with the assumptions explained in each lesson.

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How it works

Ideal series circuit: fixed 100 Ω, a sine-wave source with 1 V peak, and no startup or parasitic effects. This is a teaching model, not a tested radio circuit.

f0 = 1/(2π√(LC)). L is inductance, C capacitance, f0 resonant frequency. XL = 2πfL and XC = 1/(2πfC) are coil and capacitor reactance at drive frequency f. Current peaks when XL = XC. The source amplitude is a peak value, not an average. The net reactance is XL − XC: these are positive magnitudes with opposite effects, so equality cancels them.

Difficulty

Build · Observe
Power on at 100 mH, 100 nF and 1000 Hz. Find a natural frequency about 1591.55 Hz.
Need a hint?
100 mH; 100 nF; 1000 Hz → 1591.55 Hz
Explore · Adjust
Keep 100 mH and 100 nF; tune drive frequency for peak current at least 9.9 mA.
Need a hint?
100 mH; 100 nF; 1590 Hz → 9.998 mA
Solve it · Discover the limit
At 100 mH and 2500 Hz, choose C for a natural frequency 2450–2550 Hz and peak current at least 9 mA.
Need a hint?
100 mH; 40 nF; 2500 Hz → 2516.46 Hz; 9.793 mA

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