A photon is an elementary particle, the quantum of the electromagnetic
interaction and the basic unit of light and all other forms of
electromagnetic radiation. In other words a photon is a little packet
of energy which can carry electromagnetic radiation. It is also the
force carrier for the electromagnetic force. The effects of this force
are easily observable at both the microscopic and macroscopic level,
because the photon has no rest mass; this allows for interactions at
The electron is a subatomic particle carrying a negative electric
charge. It has no known components or substructure. Therefore, the
electron is generally believed to be an elementary particle.
The intrinsic angular momentum (spin) of the electron is a
half-integer value in units of ħ, which means that it is a fermion.
The antiparticle of the electron is called the positron. The positron
is identical to the electron except that it carries electrical and
other charges of the opposite sign. When an electron collides with a
positron, both particles may either scatter off each other or be
totally annihilated, producing a pair (or more) of gamma ray photons.
Electrons, which belong to the first generation of the lepton particle
family, participate in gravitational, electromagnetic and weak
interactions. Electrons, like all matter, have quantum mechanical
properties of both particles and waves, so they can collide with other
particles and be diffracted like light. However, this duality is best
demonstrated in experiments with electrons, due to their tiny mass.
Since an electron is a fermion, no two electrons can occupy the same
quantum state, in accordance with the Pauli exclusion principle.
One electron has a charge of –1.602e-19 C
mass of electron is 9.1e-31 kg
The proton is a subatomic particle with an electric charge of +1
elementary charge. One or more protons are present in the nucleus of
each atom, along with neutrons. The proton is also stable by itself
and has a second identity as the hydrogen ion, H+. The proton is
composed of three fundamental particles: two up quarks and one down
One proton has a charge of +1.602e-19 C
mass of proton is 1.6726e−27 kg
diameter 1.6-1.7 Fm
The neutron is a subatomic particle with no net electric charge
and a mass slightly larger than that of a proton. With the exception
of hydrogen, nuclei of atoms consist of protons and neutrons, which
are therefore collectively referred to as nucleons. The number of
protons in a nucleus is the atomic number and defines the type of
element the atom forms. The number of neutrons is the neutron number
and determines the isotope of an element. For example, the abundant
carbon-12 isotope has 6 protons and 6 neutrons, while the very rare
radioactive carbon-14 isotope has 6 protons and 8 neutrons.
While bound neutrons in stable nuclei are stable, free neutrons are
unstable; they undergo beta decay with a mean lifetime of just under
15 minutes. Free neutrons are produced in nuclear
fission and fusion. Dedicated neutron sources like research reactors
and spallation sources produce free neutrons for use in irradiation
and in neutron scattering experiments.
Mass of neutron is 1.6749e−27 kg
Black Body Radiation
Center of Mass
Flow in fluids
Parts, Analog IC
SI (metric) prefixes