Eddy currents - explanation of drag force

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Chetvorno

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Eget arbete

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https://sewiki.info/b/c5c3c

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Wikimedia Commons

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1752 x 967 Pixel (33926 Bytes)

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Diagram showing the forces on an electron in a metal sheet moving to the right under a magnet ${\displaystyle \mathbf {N} }$, explaining eddy currents, and where the drag force on the sheet comes from. The red dot ${\displaystyle \mathbf {e} _{\text{1}}}$ shows an electron in the metal under the magnet right after it has undergone a collision, and ${\displaystyle \mathbf {e} _{\text{2}}}$ shows the same electron after it has been accelerated by the magnetic field. On average at ${\displaystyle \mathbf {e} _{\text{1}}}$ the electron has the same velocity as the sheet ${\displaystyle \mathbf {v} }$ (black arrow). in the ${\displaystyle +\mathbf {x} }$ direction. The magnetic field (${\displaystyle \mathbf {B} }$, green arrow) of the magnet's North pole N is directed down in the ${\displaystyle -\mathbf {y} }$ direction. The magnetic field exerts a Lorentz force on the electron (pink arrow) of ${\displaystyle \mathbf {F} _{\text{1}}=-e(\mathbf {v} \times \mathbf {B} )}$, where e is the electron's charge. Since the electron has a negative charge, from the right hand rule this is directed in the ${\displaystyle +\mathbf {y} }$ direction. At ${\displaystyle \mathbf {e} _{\text{2}}}$ this force gives the electron a component of velocity in the sideways direction (${\displaystyle \mathbf {v} _{\text{2}}}$. black arrow) The magnetic field acting on this sideways velocity, then exerts a Lorentz force on the particle of ${\displaystyle \mathbf {F} _{\text{2}}=-e(\mathbf {v} _{\text{2}}\times \mathbf {B} )}$. From the right hand rule, this is directed in the ${\displaystyle -\mathbf {x} }$, opposite to the velocity ${\displaystyle \mathbf {v} }$ of the metal sheet. This force accelerates the electron giving it a component of velocity opposite to the sheet. Collisions of these electrons with the atoms of the sheet exert a drag force on the sheet.

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CC0

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Creative Commons Zero, Public Domain Dedication