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Spriteling
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Homework Statement
A wire with uniform charge density λ per unit length is bent into a ring of radius a and rotates with angular velocity ω about an axis through its centre and perpendicular to the plane of the ring. Find the magnetic field on the axis at a distance z from the ring.
Homework Equations
The magnetic field at a distance z from a ring with current I flowing through it is
[tex]B = \frac{\mu_0 I a^2}{2(a^2 + z^2)^{3/2}}\hat{z}[/tex]
The Attempt at a Solution
I assumed that the magnetic field would be the same as in a stationary ring with current I, where in this case I would be given by λωa. However, the solution appears to be less than this by a factor of 1/2 and I am completely at a loss as to where this extra 1/2 comes from.