Quark Model of the Neutron According to the quark model of fundamental particles, neutrons-the neutral particles in an atom's nucleus-are composed of three quarks. Two of these quarks are "down" quarks, each with a charge of ; the third quark is an "up" quark, with a charge of . This gives the neutron a net charge of zero. What is the electric potential energy of these three quarks, assuming they are equidistant from one another, with a separation distance of ? I don't even know where to start! Help!