How does tuning a radio pick out just one station from all the signals in the air?
The radio's LCR circuit is set to resonance by adjusting C (or L).
The radio's LCR circuit is set to resonance by adjusting C (or L). At the resonant frequency f = 1/(2π√LC), the inductive and capacitive reactances cancel, the impedance drops to just R, and the current for that one frequency is maximum. All other stations are far from resonance, so they produce tiny currents and are ignored. Turning the dial changes C and re-tunes the resonance.
Key point
At resonance f = 1/(2π√LC), impedance is minimum so that station's current peaks.
Common mistake
thinking resonance maximises impedance and blocks the signal.
Memory tip
tune C until the wanted frequency resonates — current peaks there.
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