Energy Stored in Magnetic Field of Solenoid

AI Thread Summary
The discussion centers on calculating the energy stored in the magnetic field of a solenoid with a specified length and diameter. The user initially applies the formula U=(1/2)(B^2)(area*length)/(u) but encounters an issue with their calculated result. A suggestion is made to verify the value used for permeability in the equation. The user acknowledges the oversight and expresses gratitude for the assistance. The conversation highlights the importance of accurate constants in physics calculations.
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Homework Statement


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?


Homework Equations



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

The Attempt at a Solution


I discovered how to derive the bottom equation from the top equation from http://hyperphysics.phy-astr.gsu.edu/HBASE/electric/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,
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Check the value you use for permeability.
 
Kurdt said:
Check the value you use for permeability.

Oh wow do I feel stupid now... Thanks for the help!
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