Hey guys(adsbygoogle = window.adsbygoogle || []).push({});

First off id like to say this is an awesome forum from what ive seen, and has since been bookmarked at the top of my list as i am an avid physics enthusiast (but **** at spelling :) )

Ok, to the nitty gritty. I have the following circuit (attached)

Now, there are two questions. Firstly to find the differential equation satisfied by Q(t) (where the charge for t=0 in the cap is Qmax).

Now i managed to get the following which i think is right (sorry i dunno how to do your cool maths type stuff)

Q/C -(dQ/dt)(R) - (L)(2nd derivative of q wrt t) = 0 (Kirchoff's loop law)

Now unfortunately i was sick the week we did DEs in maths :P so your gonna have to go slow. Im currently reviewing the notes from that part but the guys handwriting is shocking so its probably easier to just listen to you guys.

My first question is obviously is it right and is that the neatest most simplified form i can get it into?

Next question is i need to show that Q(t)=Qmax(e^(-at))(Cos(wt)) satisfies this differential equation. Now im assuming im not meant to simply take the required derivatives and sub it into the first eqn and see if it works, because that would be an algerbraic nightmare and ive seen glimpses of some nifty DE tricks so please, regail me!

Cheers guys!

-G

EDIT: Sorry guys, didnt see the no homework thing. feel free to move n stuff

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# LCR Circuit with Capacitor as diminishing power source

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