Electrons And Photons

Electron: Meaning, Definition & Formula

The atom is made up of three particles: electrons, protons and neutrons. The electron is a subatomic particle that carries a negative charge. Electrons are bound to the nucleus of the atom in, what are called, sub-shells. There are free electrons too which are not bound to any atom. Electrons are represented as e or ß. As mentioned earlier, electrons are negatively charged and is measured in Coulomb (the charge of an electron is given as \(1.60 x 10^{-19}C\).9Among the three constituents of an atom, electrons have the lowest mass. The mass of one electron is around 1,800 times lesser than a proton. If calculated, it comes to 9.10938356 × 10-31 kilograms.

Electron wavelength

The wavelength of an electron was first measured by Louis de Broglie. He used the concepts of Einstein’s formula, and Planck’s constant to calculate it. The equation which measures the wavelength of an electron is:

\(\lambda = \frac{h}{p}\)

Where,
\(\lambda\) is the wavelength.
\(h\) is Planck’s constant.
\(p\) is the momentum of the electron.

Photon: Meaning, Definition & Formula

Photon is a type elementary particle which has a zero rest mass and moves with a speed of light in the vacuum. A photon is the “quantum of electromagnetic radiation”. In other words, it is the smallest and the fundamental particle of an electromagnetic radiation. A photon has no mass, no electric charge and it is a stable particle.  These particles possess wave-particle duality. It has 2 polarization states. Photos do not obey the Pauli’s Exclusion Principle. Photons are emitted in natural processes. For example, during a nuclear, molecular and atomic transition to a level that is lower, various photons with different levels of energy are emitted ranging from radio waves to gamma rays. They are also emitted when a particle and its antiparticle are annihilated. The energy and momentum of a photon are related by the equation E = pc

where p is the momentum of vector p, This comes from the equation

\(E^{2}=p^{2}c^{2}+m^{2}c^{4}\)

Photon’s energy and momentum depend on its frequency(v) and wavelength(λ).

\(E=\frac{hc}{\lambda }\)

Photon also has a quantity called spin angular momentum that does not depend on its frequency.

Light, for example, is an electromagnetic radiation. Photons can be said to be the fundamental particles of light. It can be said that light is carried over space by photons.

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It must be remembered that photons describe the properties of the particles of a wave and not the overall properties of the wave itself. Also , as photon is essentially nothing but energy, it has no mass whatsoever.

Difference Between Photon and Electron

Photons and electrons are both fundamental particles, the former of electromagnetic waves and the latter of atoms. Together, they are can cause the flow of electricity. However, they are different in many aspects:

Electron Photon
It is matter. It is energy.
It has mass. It has no mass.
It carries a negative charge. It doesn’t carry any charge.
The speed of an electron can be zero or anything under the speed of light. It is impossible for an electron to achieve the speed of light. Photon travels at the speed of light.

Practise This Question

Compare the gravitational forces exerted by the Sun and the moon on the Earth. Which one exerts a greater force on the Earth? (Given: mass of the Sun, Ms=4×1031 kg, mass of moon, Mm=6.3×1022 kg, distance between the Sun and the Earth, r=1.3×1012 m and the distance between moon and the Earth, r=4.5×108 m).