How do we know protons, neutrons and electrons exist?

In summary, the conversation discusses the existence of protons, neutrons, and electrons and the concept of positive and negative charge. The linked website explains the history of the atom and the discovery of these particles. The conversation also mentions the existence of 6 types of color charges and the mystery surrounding fractional charge. The exact cause and nature of charge is still unknown, but it is considered one of the basic properties of matter, along with mass.
  • #1
ascendant
9
0
How do we know protons, neutrons and electrons exist? And what exactly is a positive or negative charge?... meaning what is it that makes it positive or negative.
 
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  • #3
We know that there are two types of electric charges. Which one you call positive and which one you call negative is purely a convention. There are some symmetries in particle physics that tell you that there really are exactly two types of electric charges.

In contrast, there are 6 types of color charges, which are responsible for nuclear forces. They are conventionally called red, green, blue, anti-red, anti-green, and anti-blue. These are just names, though. No relation to visible colors. So there is no fundamental reason why there should be just "positive" and "negative" electric charge, at least none that we see so far, but there are exactly two.

What actually causes charge, and why it can only change by whole numbers is still unknown. Fractional charge of quarks is also a big mystery so far. They can still only change their charge by 1, but it is a flip between +2/3 and -1/3, which is a bit strange.
 
  • #4
thank you Sakha. And K^2 sorry but you confused me. I basically mean what is a charge? what is it about the object that gives off this thing that we call charge.
 
  • #5
That's what we don't know.
 
  • #6
ascendant said:
I basically mean what is a charge? what is it about the object that gives off this thing that we call charge.

I think it's helpful to visualize these patterns:

Mass and charge are two basic properties of matter.

Mass - all matter has it. Charge - some matter has it and some doesn't.

Mass - there is just one kind, so it always has a positive sign. Charge -there are two kinds, so we give it positive and negative signs.

Due to mass, gravitational force always attracts. Due to charge, electric force sometimes attracts and sometimes repels.
 

1. How do we know protons exist?

Protons were first discovered by Ernest Rutherford in 1917 through his gold foil experiment. He observed that some alpha particles were deflected at large angles, indicating the presence of a dense, positively charged particle in the atom's nucleus. Later experiments, such as the discovery of isotopes and the development of particle accelerators, further confirmed the existence of protons.

2. How do we know neutrons exist?

Neutrons were first hypothesized by James Chadwick in 1932 to explain the discrepancy between the atomic mass and atomic number of elements. His experiments with beryllium and alpha particles led to the discovery of neutrons, which have no charge but contribute to the atomic mass of an atom. Subsequent experiments, such as neutron scattering, have further confirmed the existence of neutrons.

3. How do we know electrons exist?

Electrons were first discovered by J.J. Thomson in 1897 through his cathode ray experiment. He observed that a beam of particles with a negative charge was produced when an electric current was passed through a vacuum tube. Later experiments, such as the photoelectric effect and the double-slit experiment, have further confirmed the existence of electrons and their wave-particle duality.

4. How do we know the properties of protons, neutrons, and electrons?

The properties of protons, neutrons, and electrons have been studied extensively through various experiments, such as spectroscopy, scattering experiments, and particle accelerators. Scientists have determined their masses, charges, and other characteristics through these experiments, providing a deeper understanding of the fundamental building blocks of matter.

5. How do we know protons, neutrons, and electrons make up atoms?

The discovery of protons, neutrons, and electrons provided evidence for the existence of atoms, which were first proposed by Greek philosophers in ancient times. Later experiments, such as the development of the periodic table and the discovery of isotopes, further confirmed that atoms are composed of protons, neutrons, and electrons. The understanding of atomic structure and behavior has been continually refined through advancements in technology and scientific research.

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