Calculating the frequency based on LC circuit

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Discussion Overview

The discussion revolves around calculating the resonant frequency of an LC circuit used in a lightning detector, specifically focusing on the values of the inductor and capacitor provided in a referenced design. Participants explore the implications of unit conversions and mathematical expressions in the frequency calculation.

Discussion Character

  • Technical explanation, Mathematical reasoning, Conceptual clarification

Main Points Raised

  • One participant presents a calculation for the resonant frequency using the formula f = 1/2π√(LC) with given values of 10 mH and 10 pF, arriving at an answer of 5 Hz.
  • Another participant questions the initial calculation, suggesting that SI prefixes may not have been properly considered and that brackets might be missing in the equation.
  • A subsequent reply details the correct interpretation of the SI units, clarifying that 10 mH is 10×10^(-3) H and 10 pF is 10×10^(-12) F, leading to a recalculated frequency of approximately 503.3 kHz.
  • The original poster acknowledges the error in their calculation after receiving feedback.

Areas of Agreement / Disagreement

Participants generally agree on the correct approach to calculating the resonant frequency, but there is an initial disagreement regarding the accuracy of the first calculation and the interpretation of SI units.

Contextual Notes

The discussion highlights potential limitations in the original calculation, including the need for careful attention to unit conversions and the correct application of mathematical operations.

guns
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Hi all,

I am currently building up a lightning detector based on this website: http://www.techlib.com/electronics/lightningnew.htm
as the diagrams shows, the resonance tank included a 10mH inductor and a 10pF capacitor.
As I want to calculate the resonant frequency (using the formula f = 1/2pi*sqrt(LC)), the answer was 5Hz, which is far from the desired range (should be around 200kHz)
is there any mistake in my calculation or concept? Thanks for your help.

Guns
 
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How did you get your answer? Did you consider the SI prefixes (milli, pico)?
I think there are brackets missing in your equation.
 
mfb,
I did it this way:
1/2pi*sqrt(10^(-3)*10^(-12))
which approxmately equals to 5 Hz.
 
Following up on mfb's post, you're missing brackets and are using the wrong values for the SI units:

10 mH = 10*10^(-3) H
10 pF = 10*10^(-12) F

1/(2*pi*sqrt(10*10^(-3)*10*10^(-12))) Hz = 503.3*10^3 Hz = 503.3 kHz
 
oh my, silly me.
Thanks mfb and milesyoung!
 

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