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Electromagnetism}LC Circuit

The form for a simple harmonic oscillator is m\ddot{x} + kx =0, which one can obtain from Hooke's Law. Comparing this to the LC circuit equation L\ddot{Q}+Q/C=0, one sees that L \Leftrightarrow m and 1/C \Leftrightarrow k and Q \Leftrightarrow x. This is choice (B).

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Comments
theperiodictable
2014-10-23 11:05:59
One good thing to consider for this problem is the following: the only thing you can have a derivative of is x, since m and k are constants, so Q must be x.NEC
bslugger360
2013-08-11 16:21:51
Another thought that helped me was looking at the energy of a spring and the energy of a capacitor:

U_{capacitor} = \frac{Q^2}{2C}

U_{spring} = \frac{kx^2}{2}

From this it's pretty clear that Q\Rightarrowx and C\Rightarrow1/k, making B the only possible answer.
NEC
mrTrig
2010-11-09 00:43:49
Something nice to remember \omega = \frac{1}{\sqrt{LC}} for LC Circuits. And from hook's \omega = \sqrt{\frac{k}{m}}. Thus L and C must be inversely related and must be related to either k or m. Only B satisfies. NEC
carl_the_sagan
2008-11-07 19:48:26
A really cheesy way is to totally disregard the question and just look at the answers. Typically on a question like this they are going to have to repeat the correct value for each column a few times.

so "m" is repeated in L, "1/k" is repeated in C, and "x" is repeated in Q. The only answer which lines all these multiple-occurring rows is B.

Granted this has nothing to do with physics, but this isn't about physics, its about getting the right answer.
amber
2014-10-22 23:27:03
I went with this route too. I figured if there were two that were close I could reason it out, but I didn't have to do that.
UNKNOWNUMBER
2018-10-18 21:06:34
I don\'t think this works all the time--I would say you just got lucky.
NEC

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One good thing to consider for this problem is the following: the only thing you can have a derivative of is x, since m and k are constants, so Q must be x.

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