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thatguy14
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Homework Statement
We will see (in Chap. 5) that the magnetic field can be derived from a vector potential function as
follows:
B = ∇×A
Show that, in the special case of a uniform magnetic field B[itex]_{0}[/itex] , one possible
vector potential function is A = [itex]\frac{1}{2}[/itex]B[itex]_{0}[/itex]×r
MUST USE TENSOR NOTATIONm also B0 is constant (uniform magnetic field)
Homework Equations
ε[itex]_{ijk}[/itex]ε[itex]_{klm}[/itex] = δ[itex]_{il}[/itex]δ[itex]_{jm}[/itex] - δ[itex]_{im}[/itex]δ[itex]_{jl}[/itex]
The Attempt at a Solution
I have tried a bunch of different things but I am missing something near the end.
Here is what I have
B = (∇×A)[itex]_{i}[/itex]
B = ε[itex]_{ijk}[/itex]∂[itex]_{j}[/itex]A[itex]_{k}[/itex]
B = ε[itex]_{ijk}[/itex]∂[itex]_{j}[/itex] ([itex]\frac{1}{2}[/itex]ε[itex]_{klm}[/itex]B[itex]_{0l}[/itex]r[itex]_{m}[/itex])
B = [itex]\frac{1}{2}[/itex]ε[itex]_{ijk}[/itex]ε[itex]_{klm}[/itex]∂[itex]_{j}[/itex]B[itex]_{0l}[/itex]r[itex]_{m}[/itex])
where ε[itex]_{ijk}[/itex]ε[itex]_{klm}[/itex] = δ[itex]_{il}[/itex]δ[itex]_{jm}[/itex] - δ[itex]_{im}[/itex]δ[itex]_{jl}[/itex]
So B = [itex]\frac{1}{2}[/itex][δ[itex]_{il}[/itex]δ[itex]_{jm}[/itex] - δ[itex]_{im}[/itex]δ[itex]_{jl}[/itex]]∂[itex]_{j}[/itex]B[itex]_{0l}[/itex]r[itex]_{m}[/itex]
Changing indicies gives (noting that the derivative of constant = 0 and using the product rule)
B = [itex]\frac{1}{2}[/itex][B[itex]_{0i}[/itex]∂[itex]_{m}[/itex]r[itex]_{m}[/itex] - B[itex]_{0l}[/itex]∂[itex]_{l}[/itex]r[itex]_{i}[/itex]]
And that's where I am stuck. What comes next? I am assuming that with the last term there, l and i have to be equal (because if they aren't then it equals 0) and I think I have to introduct the krockner delta somewhere but I am unsure. Any help would be greatly appreciated.
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