resistance in an LRC circuit used to calculate time constant

• To: tesla-at-pupman-dot-com
• Subject: resistance in an LRC circuit used to calculate time constant
• From: "Alfred C. Erpel" <alfred-at-erpel-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
• Date: Sun, 12 Mar 2000 08:56:42 -0700
• Approved: twftesla-at-uswest-dot-net
• Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Hello,
 
 
    An LRC circuit has three components of resistance; the internal resistance
of the inductor, the internal resistance of the capacitor, and resistance in
the wiring connecting the inductor and capacitor.
The resonant frequency of this LRC circuit is 1 / [2 * PI * SQRT(L * C)]
regardless of the total resistance in the circuit.
 
a)   The time constant of a capacitor is C * R.
b)   The time constant of an inductor is L / R.
 
    In the context of this resonant circuit, when you calculate the time
constants of each device, how do you figure R?  Is R just the resistance
internal to the device (inductor or capacitor) or do you add up the total R for
the circuit (all three components) to determine R for the equations above? How
do you account for the R in the circuit external to both devices?
 
 
Regards,
Alfred Erpel
 
 

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