Quark Model of the Neutron The neutron is a particle with zero charge. Nonetheless, it has a nonzero magnetic moment with z component 9.66 X 10-27 A. m2. This can be explained by the internal structure of the neutron. A substantial body of evidence indicates that a neutron is composed of three fundamental particles called quarks: an €œup€ (u) quark, of charge + 2e/3, and two €œdown€ (d) quarks, each of charge - e/3. The combination of the three quarks produces a net charge of 2e/3 - e/3 - e/3 = 0. If the quarks are in motion, they can produce a nonzero magnetic moment. As a very simple model, suppose the u quark moves in a counter clockwise circular path and the d quarks move in a clockwise circular path, all of radius T and all with the same speed v (Fig.).
(a) Determine the current due to the circulation of the u quark.
(b) Determine the magnitude of the magnetic moment due to the circulating u quark.
(c) Determine the magnitude of the magnetic moment of the three quark system. (Be careful to use the correct magnetic moment directions.)
(d) With what speed v must the quarks move if this model is to reproduce the magnetic moment of the neutron? Use T = 1.20 X 10-15 m (the radius of the neutron) for the radius of the orbits.

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