Question Video: Listing Particles in Order of Decreasing Mass Physics

List the following particles in order from the greatest to the least mass: positron, neutron, helium nucleus, photon, neutrino


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.

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