What is the energy of a toroidal solenoid with given dimensions and current?

[iwan97]

Homework Statement

[/B]
N=600 (number of loops)
a₁=200mm
a₂=240mm
h=40mm
δ=1,5mm or l₀
S₀=1,1*S (Cross sectional area)
B₀=1,2T

I need to find energy of toroid and currect going through it.
Solution: W=4,08J, I=6,44A

2. The attempt at a solution

So far I managed to calculate S and S₀:
S=(a₂-a₁)*h
S=0,0016m²
S₀=1,1*S
S₀=0,00176m²I tried to find energy using this formula but it's not correct:
W₀=B₀²*S₀*l₀/2*μ₀
W₀=1,51J

W=B*H*S*(l-l₀)/2 (B and H are from the graph)
W=4,76J

Formula for current is I=NH/l but since nothing is correct I didn't bother to try and calculate it.

 

[rude man]

I see nothing wrong with your formula for W₀ and W unless you made an arithmetic error which I suspect you did. For example, I got W = 2.34J.
Your formula I=NH/l is wrong however so not using it was ironically a good move!

 

[iwan97]

Never mind. I figured it out. Thanks !