Video Transcript
In this video, we’ll learn about
quarks, a type of fundamental particle. We’ll learn about the properties of
quarks and how they can combine to create larger particles, like the proton and
neutron. This is an atom of helium. Its nucleus contains two protons
and two neutrons. Surrounding the nucleus are the two
electrons in the electron cloud. Now, which of these three types of
particle are fundamental or elementary particles?
Fundamental or elementary particles
are particles that are not made of smaller particles. You might have thought that the
proton, neutron, and electron are all fundamental particles. While that’s true for the electron,
the neutron and proton are not. If we could zoom in on these three
particles and take a look at them somehow, we would see that the proton and neutron
are each made of three smaller particles. These smaller fundamental particles
that make up the proton and neutron are called quarks.
As we can see from this diagram,
there are different kinds of quarks. The different kinds of quarks are
called flavors, and yes that’s the scientific term. There are six flavors of quarks:
up, down, charm, strange, top, and bottom. Quarks, together with the other
fundamental particles, make up what’s called the standard model. The standard model is made of some
particles that are familiar to us, like the quarks, the electron, and the photon, as
well as many other particles that we probably haven’t seen before.
These particles on the left in the
standard model are called fermions. Fermions are the building blocks of
matter, just like the quark and the electron that make up atoms. These particles on the right in the
standard model are bosons. Bosons are responsible for the
fundamental forces of nature. Photons, for example, are emitted
or absorbed whenever there’s a change in electromagnetic radiation. We don’t need to worry about the
details of the standard model because this is getting well into the realm of
particle physics. So let’s move on to the properties
of quarks, starting with the electrical charge.
To express the charge of quarks,
we’ll use elementary charges, denoted by the letter 𝑒. For reference, the charge on the
proton is positive one 𝑒 and the charge of the electron is negative one 𝑒. The electrical charge of quarks
depends on their flavor. The up, charm, and top quarks all
have a charge of positive two-thirds 𝑒, while the down, strange, and bottom quarks
have charges of negative one-third 𝑒. In nature, quarks never exist on
their own. Quarks are always found in groups
of two or three. Quarks are held together by the
strong force. A group of quarks held together by
the strong force creates a larger particle. These particles that are made from
quarks are collectively known as hadrons. Two examples of hadrons that we’re
familiar with are the proton and neutron.
Let’s see which quarks make up the
proton and neutron. The proton is made of two up quarks
and a down quark. The neutron is made of one up quark
and two down quarks. We can calculate the charge of the
proton and neutron using the charges of the quarks that they’re made of. The proton is made of two up
quarks, which each have a charge of positive two-thirds 𝑒, and one down quark,
which has a charge of negative one-third 𝑒. This gives us a charge of positive
one for the charge of the proton, which is what we’d expect. If we add up the charges of the up
quark and two down quarks that make up the neutron, we get zero, again what we’d
expect for the charge of the neutron.
Now we’ve learned what quarks are,
the different flavors of quarks, and the properties of quarks. So let’s test our knowledge with a
problem.
Which of the following is not a
type of quark? (A) Up, (B) bottom, (C) strange,
(D) left, or (E) down.
Quarks are a type of fundamental
particle. Quarks combine to make other
particles, like the proton and neutron. There are six types of quarks,
which are called flavors. The different flavors of quarks are
up, down, charm, strange, top, and bottom. This question asked us to identify
which answer choice was not of type or flavor of quark. Looking through our answer choices,
we’ll see that though many of the quarks have directional names, left is not one of
them.
A composite particle is composed of
two up quarks and one down quark. What is the overall electrical
charge of this particle?
A quark is a type of fundamental
particle. A fundamental particle is a
particle that’s not made of smaller particles. In nature, quarks never exist on
their own. They combine to create other larger
particles. The composite particle in this
question is made of two up quarks and one down quark. The particle that’s made of two up
quarks and a down quark is the proton. The overall electrical charge of
the proton is positive one.
If we didn’t identify this
composite particle as the proton, we can still answer this question. We can calculate the overall
electrical charge of the particle using the charges of the quarks. The up quark has a charge of
positive two-thirds, and the down quark has a charge of negative one-third. If we add up the charges for the
quarks that make up the composite particle, we get positive one. So either way we solve this
question, the overall electrical charge of the composite particle is positive
one.
Now let’s sum up this video with
the key points. Quarks are a type of fundamental
particle that makes up protons and neutrons. There are six types of quarks,
which are called flavors. The six flavors of quarks are up,
down, charm, strange, top, and bottom. The up, charm, and top quarks have
a charge of positive two-thirds 𝑒, and the down, strange, and bottom quarks have a
charge of negative one-third 𝑒. Protons are made of two up quarks
and one down quark, while neutrons are made of one up quark and two down quarks.
