Absorbing extremely narrow range of freq

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granpa
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A hydrogen atom exposed to a continuum of frequencies will only absorb those frequencies that correspond to allowed transitions of the electron. As I understand it, these absorption lines are very thin. Frequencies only slightly off are not absorbed at all.

How difficult would it be to make an electronic circuit with a single absorption line (i.e. that could absorb such a narrow range of frequencies)?
 

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http://en.wikipedia.org/wiki/File:Resonance.PNG
800px-Resonance.PNG
 
http://en.wikipedia.org/wiki/Resonance#Q_factor

The quality factor or Q factor is a dimensionless parameter that describes how damped an oscillator or resonator is,[8] or equivalently, characterizes a resonator's bandwidth relative to its center frequency

so it would need a very high Q factor. In other words, virtually no damping
 
Yes.

It is possible to make resonators with extremely high Q values (billions), meaning their linewidth will be much smaller (and the decay time much longer) than that of many atomic levels (the linewidth it atoms can vary over many orders of magnitude, in some cases the decay times are extremely short leading to very wide spectral widths).