On the proton-equals-+1 scale, what charge does the down quark carry?
The proton's charge is +1, and a proton is nothing but three quarks. So the quarks must carry that charge between them. Do the numbers actually work out?
You have every number you need. The up quark carries +2/3; the down quark carries −1/3. The proton is uud; the neutron is udd.
Test it on the proton, uud. The three charges are +2/3, +2/3, and −1/3. Add them: (+2/3) + (+2/3) + (−1/3) = +1. The total is +1, exactly the proton's known charge. The check passes.
A neutron's quark content is udd. Calculate the total charge of its quarks, and check it against the neutron's known charge.
Write down the values in the question:
udd: u = +2/3, d = −1/3, d = −1/3
Write down the equation:
total charge = sum of the quark charges
Substitute in the values:
total charge = (+2/3) + (−1/3) + (−1/3)
Simplify:
total charge = 0
The neutron's known charge is 0, and the quark charges add to 0. The check passes.
Here are six fast totals. Each up quark adds +2/3; each down quark adds −1/3.
Two up quarks sit together. What is their total charge?
One up quark and one down quark sit together. What is their total charge?
Three down quarks sit together. On the proton-equals-+1 scale, what is their total charge? Enter the number.
Two down quarks sit together. What is their total charge?
Three up quarks sit together. On the proton-equals-+1 scale, what is their total charge? Enter the number.
You add up a proton's quark charges and get +2/3. Does your total match the proton's charge?
Which calculation finds the neutron's charge from its quark content?
A group holds two up quarks and two down quarks. What is the group's total charge?
A student lists a proton's quarks as one up quark and two down quarks. Which check shows the list is wrong?