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LC circuit help

by Liquidxlax
Tags: capacitor, circuits, electricty, inductor
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Liquidxlax
#1
Mar30-11, 09:42 AM
P: 322
1. The problem statement, all variables and given/known data

A solenoid with self-inductance L=2H and carrying a steady current of 1 A has the current source suddenly turned off. What is the minimum capacitance that should be connected across the terminals of the solenoid in order to prevent the potential difference generated by collapse of the mag field from rising above 300V.

2. Relevant equations

1/sqrt(LC) = resonance frequency

LD^2 + I/C = 0


3. The attempt at a solution

Are the capacitor and solenoid in series or parallel and I'm not sure exactly where to start.

Sorry that I don't have any work to show.
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gneill
#2
Mar30-11, 10:42 AM
Mentor
P: 11,685
Connected across the terminals implies that they are in parallel. However, if the solenoid and capacitor are the only remaining components, then one might argue either way.

You might consider the energy stored in the magnetic field of the solenoid, and what would happen if it were to all be dumped onto the capacitor during the first cycle of oscillation.
Liquidxlax
#3
Mar31-11, 07:10 PM
P: 322
i guess they're are parallel, but i'm not sure how to find the energy stored? Don't i need the time derivative of current????

gneill
#4
Mar31-11, 07:16 PM
Mentor
P: 11,685
LC circuit help

Energy stored in an inductor:
http://hyperphysics.phy-astr.gsu.edu...ic/indeng.html

Energy stored in a capacitor:
http://hyperphysics.phy-astr.gsu.edu...ic/capeng.html

So, (1/2) L I2 and (1/2) C V2
Liquidxlax
#5
Apr2-11, 11:31 AM
P: 322
Quote Quote by gneill View Post
Energy stored in an inductor:
http://hyperphysics.phy-astr.gsu.edu...ic/indeng.html

Energy stored in a capacitor:
http://hyperphysics.phy-astr.gsu.edu...ic/capeng.html

So, (1/2) L I2 and (1/2) C V2
aww bugger, i knew the energy stored in a capacitor, couldn't find energy stored in an inductor. thank you very much


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