like the title says. How do I input this formula into a calculator?
L = 1 / (4π^2f^2C)
Here is the entire question
Determining Inductance for a Resonant Frequency of 14.25 MHz and C = 44 picofarads
Thanks,
VE7VP
Paul, I see my formula notation on the AA site is confusing. I’ve fixed it and made it more clear. The correct formula is
L = 1/(4π²f²C)
…or…
L = (4π²f²C)-1
…and in your calculator, type…
(4 x π² x (14.25 x 106)² x (44 x 10-12))-1
…and you should see 2.8 microhenries.
IMPORTANT NOTE TO ANYONE READING: You do not have to memorize this formula. Just memorize 2.8 microhenries and save yourself ten minutes.
Thanks Reg! It makes a hell of a lot more sense now lol
Doing a practice exam and I came across this question:
What is the value of capacitance (C) in a series R-L-C circuit, if the circuit resonant frequency is 14.25 MHz and L is 2.84 microhenrys?
It’s different then the above question I had asked about. No 2.8 microhenrys in the multiple choice answers. So it seems to me we do have to know this formula for the exam. Please correct me if I’m wrong.
@Paul, this is what I was trying to say in the study group. All the questions from this section ask for resonant frequency except these two stupid questions asking capacitance and inductance.
Option 1
My opinion is that you should just memorize the answers to these two questions:
2.8 microhenries
44 picofarads
If you see 2.8 microhenries anywhere on your test as an answer, it is correct. If you see 44 picofarads anywhere on your test as an answer, it is correct (although 44 picofarads does appear in another question somewhere, but that’s not relevant).
Option 2
If you want, you can memorize the two additional formulas instead:
C = 1/(4π²f²L)
L = 1/(4π²f²C)
Option 3
You can also use @Mike’s method of plugging in the four answers into the main formula and seeing which one gives you the stated resonant frequency.
