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Energy Stored in Magnetic Field of Solenoid

by x^2
Tags: energy, field, magnetic, solenoid, stored
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x^2
#1
Apr16-09, 02:21 PM
P: 21
1. The problem statement, all variables and given/known data
The magnetic field inside an air-filled solenoid 39.9cm long and 2.00cm in diameter is 0.800T. Approximately how much energy is stored in this field?


2. Relevant equations

U=(1/2)LI^2
=> U = (1/2)(B^2)(area*length)/(u)

3. The attempt at a solution
I discovered how to derive the bottom equation from the top equation from http://hyperphysics.phy-astr.gsu.edu...indeng.html#c2

The derivation on the site seems to make sense, but when I try to use the bottom equation I get:
U = (1/2)(0.8^2)(Pi*0.01^2)*(0.399)/(8.85*10^-7) = 45.324 J

What am I missing here?

Thanks,
x^2
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Kurdt
#2
Apr17-09, 03:45 AM
Emeritus
Sci Advisor
PF Gold
P: 4,981
Check the value you use for permeability.
x^2
#3
Apr17-09, 01:37 PM
P: 21
Quote Quote by Kurdt View Post
Check the value you use for permeability.
Oh wow do I feel stupid now..... Thanks for the help!
x^2


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