Questions and Answers
What is the charge of an up quark and the charge of a down quark? How many quarks make up a proton and a neutron?
Quarks carry fractional electrical charges. An 'up' quark has a charge of +2/3 and a 'down' quark has a charge of -1/3. Is this consistent with what we know about protons and neutrons? Remember that protons carry an electrical charge of +1 while neutrons carry no electrical charge. We said earlier that a proton has two 'up' quarks and one 'down' quark, so it has a total charge of (+2/3) + (+2/3) + (-1/3) = +1. We also said that a neutron has two 'down' quarks and one 'up' quark, so it has a total charge of (-1/3) + (-1/3) + (+ 2/3) = 0. Happily, both the proton and the neutron 'end up' with the charge they should have.