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jtleafs33
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Homework Statement
I put this in the math forum because although it's for my EM waves class, it's a math question.
Show that the spin force can be written as:
[itex]F_{spin}=\frac{-1}{2}Im(\alpha)Im(E\cdot\nabla E^{*})=\nabla\times L_s[/itex]
Find [itex]L_s[/itex].
Where [itex]\alpha[/itex] is complex. I'm using [itex]E^{*}[/itex] to denote the complex conjugate of [itex]E[/itex]. Also, since these are all vectors, I'm omitting the arrow notation atop the vector quantities.
Homework Equations
[itex]Im(z)=\frac{1}{2i}(z-z^{*})[/itex]
The Attempt at a Solution
From the relevant equations:
[itex]Im(\alpha)=\frac{1}{2i}[\alpha-\alpha^{*}][/itex]
[itex]Im(E\cdot\nabla E^{*})=\frac{1}{2i}[E\cdot\nabla E^{*}-(E\cdot\nabla E^{*})^{*}][/itex]
Substituting in,
[itex]F_{spin}=\frac{1}{8}[\alpha-\alpha^{*}][E\cdot\nabla E^{*}-(E\cdot\nabla E^{*})^{*}]=\nabla\times L_s[/itex]
Here, in order to make a curl appear, I'd like to apply the identity:
[itex]\nabla\times(A\times B)=A(\nabla\cdot B)-B(\nabla\cdot A)+(B\cdot\nabla)A-(A\cdot\nabla)B[/itex]
However, I'm not sure what the quantity [itex][(E\cdot\nabla E^{*})^{*}][/itex] looks like... I don't know how to conjugate this and I'm stuck here for the moment.
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