Video: Understanding Composite Particles

The table shows the relative charges of the up and down quarks. If a composite particle were made up of 3 up quarks, what would the relative charge of that composite particle be?

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Video Transcript

The table shows the relative charges of the up and down quarks. If a composite particle were made up of three up quarks, what would the relative charge of that composite particle be?

Okay, so in this table, we can see that there are the up quark and down quark given in the table as well as their relative charges. The up quark has a relative charge of two-thirds. And the down quark has a relative charge of negative one-third, where, of course, relative charges are measured relative to the charge of a proton. In other words, an up quark has a charge that is the same sign as the charge on a proton, it’s positive. But the magnitude or size of that charge is only two-thirds the size of the charge on a proton. And in the same way, the down quark has a negative charge. So the sign of the charge is opposite to that of the proton. But the magnitude or size of that charge is one-third that the magnitude of the charge on a proton.

Now, we’ve been told that a composite particle is made up of three up quarks. So here they are. One, two, three. And as we know, each up quark has a relative charge of positive two-thirds. So the total charge on this composite particle is going to be positive two-thirds from one of the up quarks plus another two-thirds from the second up quark plus a final two-thirds from the third up quark. So this becomes two-thirds plus two-thirds plus two-thirds which simplifies to positive six divided by three. And that is the same thing as positive two. And hence, we can say that the total relative charge on a composite particle made up of three up quarks is positive two.

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