Question

It is now believed that protons and neutrons (which constitute nuclei of ordinary matter) are themselves built out of more elementary units called quarks. A proton and a neutron consist of three quarks each. Two types of quarks, the so-called 'up' quark (denoted by u) of charge + (2/3) e, and the 'down' quark (denoted by d) of charge (-1/3) e, together with electrons build up ordinary matter. (Quarks of other types have also been found which give rise to different unusual varieties of matter.) Suggest a possible quark composition of a proton and neutron.

Answer 1

The net charge on proton is +e. This can be obtained by $p=(\frac{2}{3}+\frac{2}{3}-\frac{1}{3})e=+e$

Hence, proton has two 'up' quark and a 'down quark'.

The net charge on neutron is 0. This can be obtained by $n=(\frac{2}{3}-\frac{1}{3}-\frac{1}{3})=0$

Hence, neutron has one 'up' quark and two 'down' quarks.