# Magnetism: Biot-Savart Law

1. Nov 30, 2005

### dekoi

Suppose an electron orbits a proton at a distance of 'r' with speed 'v'.
How could i determine the magnitude of the magnetic field at the location of the proton?

I thought it would make sense to use The Biot-Savart Law, but i dont know where to begin:
$$dB = \frac{\mu_o}{4\pi} \frac{I ds x r}{r^2}$$
(where $$ds x r$$ is a cross product of ds and r (unit vector) )

Last edited by a moderator: Nov 30, 2005
2. Nov 30, 2005

### mezarashi

You'll be doing an integration around the circumference of the orbit. The vectors ds and r will always be perpendicular so you can ignore the vector operation and focus on magnitude.

A helping relationship would be that of current and electron flow. By definition:

J = nqv

where J is the current density, n is the electron density, q is the charge, and v is the average drift velocity. Since you have only one electron, you could probably assume I = qv/C, where C is the orbit's circumference.

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