Video: Recalling the Charge of a Strange Quark

What is the relative charge of a strange antiquark?


Video Transcript

What is the relative charge of a strange antiquark?

We can start off on our solution my first talking about what a quark is, and then we’ll look into what an antiquark is, and then we’ll look into what a strange antiquark is. So first off, what is a quark? One way to start thinking about quark is to consider the nucleus of an atom, which we know is made up of protons and neutrons. Protons and neutrons it turns out are not themselves fundamental particles. They’re actually made of particles yet smaller than themselves. The name we give to those particles is quarks.

The main thing that sets quarks apart, say from other subatomic particles we would know, is that a quark carries a fractional electric charge. That may not sound unusual, but when we consider the charges we’re familiar with it, turns out that it is. We’ve come to understand electric charges coming in quantized units. The smallest unit of electric charge is that possessed by an electron, and we knew that the charge on a proton is equal and opposite to that charge on an electron. Now if we think of the charge of an electron as one — that is, a single unit of charge — that means we can write the charge of an individual proton as negative one.

Notice that for both these charges, the values are whole numbers; they’re are integers. And that is where quarks start to stand out from protons and electrons. The charge on a quark rather than being negative one or one or some multiple of these numbers is a fraction of these numbers. For example, we could have a quark with a charge, we’ll call it capital 𝑄 sub 𝑞, of two-thirds; that is, it’s not a multiple of one or negative one. This is what we mean by a fractional electric charge. And know that this number is given in terms of the charge of an electron, which we’ve normalized to one. This then gives us a bit of an understanding about what a quark is, but now what about an antiquark?

Well an antiquark is just like a quark, but opposite. For example, if we symbolized an antiquark as a 𝑞 with a line over top of it, then the charge of that antiquark would be the opposite of the charge of our quark. The charge of the antiquark would be negative two-thirds. This is generally how quarks and antiquarks work together. They have the same magnitude of quantities, but opposite sign, sort of like the charge on an electron and a proton. Knowing that, we next want to understand what a strange antiquark is. Quarks, it turns out, come in more than one variety. In fact, there are six types or flavors of quarks.

Here are those six flavors, they’re called, of quark along with their relative charge; that is, their charge relative to the charge of an electron. We have an up quark, a down quark, a charm quark, a strange quark, a top quark, and a bottom quark. Unusual names aside, we know what type or flavor of quark we want to focus on here. It’s the strange flavor of quark, which has a relative charge of negative one-third. If we were being asked for the relative charge of a strange quark, then this would be our answer, but that’s not quite the question. The question asked for the relative charge of a strange antiquark. Remember we said that antiquarks are just like quarks, except they’re opposite. So if we were to write the charge of a strange antiquark, that would be opposite the charge of a strange quark. In other words, it would be negative the quantity negative one-third or simply positive one-third. That’s the charge of a strange antiquark relative to the charge of an electron.

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