A variable capacitor (C), large inductor or solenoid (L), and 200W light bulb (R) are connected in series to 120 VAC. The inductance of the inductor can be varied by inserting an iron core, and the capacitance can be varied by a row of switches. By varying the inductance and capacitance, we can achieve the resonance of the circuit, where maximum current flows through the resistor (light bulb)
Source: MIT TechTV
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