Video Transcript
List the following particles in
order from the greatest to the least mass: positron, neutron, helium nucleus,
photon, and neutrino.
So here we’ve been given a list of
six different particles, and we need to arrange them in order from greatest to least
mass. A good place to start is with the
photon. We can recall that a photon has
zero mass. So we know that we can put photon
last on our list as we know that nothing can have less than zero mass. Next, let’s think about the
neutrino. We can recall that there are three
different types of neutrino: the electron neutrino, the mu neutrino, and the tau
neutrino. And each of these neutrino types
has an associated antiparticle, which is known as an antineutrino. These are known individually as the
electron antineutrino, the mu antineutrino, and the tau antineutrino.
Now we might recall that scientists
don’t actually know the masses of the different neutrinos. However, what we do know is that
neutrino masses are incredibly small. In fact, neutrinos have the least
mass of all massive particles. There’s actually a clue for this in
the name of the neutrino. The suffix -ino means small. Even though the type of neutrino
that we’re thinking about in this question hasn’t been specified, the fact that
neutrinos have the lowest mass of any massive particle means that we can write
neutrino just before photons at the end of our list.
We now have three particles left to
put into our list: the positron, neutron, and helium nucleus. Of these, the neutron and helium
nucleus are familiar to us from thinking about atoms. A helium nucleus is effectively an
atom of helium but without the orbiting electrons. And neutrons are the electrically
neutral particles which make up an atomic nucleus along with positively charged
protons.
Since a helium nucleus contains two
neutrons and two protons, we know that it must have more mass than just a single
neutron. But what about the positron? Well, we can recall that the
positron is the antiparticle of the electron. This means it has the opposite
charge to the electron but exactly the same mass. We can also recall that the
electron has a much lower mass than a neutron. In fact, the neutron has around
2000 times the mass of an electron. And since the positron has the same
mass as an electron, this means that a neutron has around 2000 times the mass of a
positron. This means that, of these three
remaining particles, the one with the least mass is the positron. Then weighing in at around 2000
times heavier, we have the neutron. And finally, the heaviest particle
on the list is the helium nucleus.
So now we have our completed
list. In order from greatest to least
mass, we have the helium nucleus, the neutron, the positron, the neutrino, and the
photon.
