In 1932, physicist Carl Anderson was studying cosmic rays: particles that rain down on Earth from space. One of those particles matched the electron's mass exactly. But one measurement refused to match.
In earlier grades you met the electron: the tiny particle that carries a charge of −1 on the scale where the proton's charge is +1.
Anderson's particle matched the electron in every way but one. It had the electron's mass — the same, as far as any experiment can measure. But its charge was +1, not −1: the same size as the electron's charge, with the opposite sign.
The positron is not a proton. A proton also carries a charge of +1, but a proton is almost two thousand times more massive than a positron. So two measurements pin the positron down: a mass equal to the electron's, and a charge of +1.
A particle is found with the electron's mass and a charge of +1 on the scale where the proton's charge is +1. Which particle is it?
The electron's mass plus a charge of +1 is the positron's exact profile.
The particle is a positron.
A student says a positron is just a proton under another name. What single measurement tells the two apart?
A positron and a proton both carry a charge of +1.
Their masses differ: a proton is almost two thousand times more massive than a positron.
A mass measurement tells them apart. The positron's mass equals the electron's, far below the proton's.
Anderson's 1932 particle has the electron's mass. On the proton-equals-+1 scale, what charge does it carry?
Anderson's 1932 particle carries a charge of +1. How does its mass compare with the electron's mass?
A particle has the electron's mass but the opposite charge. What is it called?
Which pair of properties defines the positron?
A positron and a proton both carry a charge of +1. Which measurement tells them apart?
A positron is compared with an electron. Which properties do the two particles share?