Magnetism is produced by circulating electric currents, but alsoby the spin of elementary particles and many atoms that are smallmagnets. An electric current I circulating in a wire of radius R,produces a magnetic field in the center of the wire of value B = uor I /) 2r). (uo - 1.26 x 10 ^ -6 T m / A).
We can use this formula as a model for three situations: theEarth, an atom of iron and the electron.
a) For Earth, R = 6,000 km and B = 5 x 10 ^ -4 T. Estimate theorder of the current that is capable of generating this field.
b) For the iron atom, the magnetic field is produced by theelectron of the last level, which is a charge of 1.6 x 10 ^ -19 Cwhich circulates with the frequency of 10 ^ 16 Hz, in a radius ofabout 10 ^ -10 m. Calculate the order of the magnetic fields in theiron atom.
c) For the electron, the 1.6 x 10 ^ -19 C charge that rotates onitself. Assume that the turning radius is the order of R = 10 ^-18m. The current is then of the order of e v / (2piR) = e f, wheref is the frequency of rotation. Using this formula, calculate thevalue of B generated by the electron.
