Question

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(B) the current; (C) the sign and concentration of charge carriers; (D) All; (E) None.
A particle of mass m and charge q is in a circular orbit (of radius R) normal to an
external field B. What is proportional to the magnetic field created at the center of its
orbit by the charge? (A) m; (B) q; (C) R; (D) B; (E) None.