Electrons and Photons

Matter

All matter is made up of atoms. John Dalton was the first scientist who postulated that when the matter is broken down, the smallest entity that can be obtained is an atom. He, however, believed that atom can no further be disintegrated. This wasn’t true as it turned out.


Today, we consider it as a drawback of Dalton’s atomic theory, because atoms are indeed made up of three fundamental particles, namely electrons, protons and neutrons. 


Electrons are the subatomic particles that carry a negative charge. Their mass is negligible. They revolve in the orbits surrounding the nucleus of an atom. These orbits are also called shells or energy levels. An electron is usually represented by the letter ‘e’. The charge on an electron is 1.6 × 10-19 C. 


Of all the subatomic particles, an electron has the lowest mass of the order of 9.1 ×10 -31 kg, which is approximately 1/1800th of a proton.


Electron Formula

An electron can also be understood in the form of electromagnetic waves. The first attempt to calculate the wavelength of an electron was made by de Broglie. 


The momentum of an electron, moving with a velocity v can be written as:


P= mv 


Then, the wavelength of an electron (λ) can be calculated using the formula: 


λ= h/p 


In this equation, h is the Planck’s constant, and p is the momentum of the electron. 


h= 6.6 × 10-34 kgm2/s


The formula written above is used to calculate the wavelength of an electron and is known as the de Broglie equation, while the calculated wavelength is called the de Broglie wavelength. 


From the formula, it can be interpreted, that an electron having a higher velocity (or momentum) will have a shorter wavelength and vice versa. 


Photon Meaning and Formula 

In quantum physics, we consider that every electromagnetic radiation is made up of small packets of energy called ‘quanta’. Since light is also an electromagnetic radiation, its beam will also be composed of billions of packets of energy, which are called photons. 


In other words, a photon is the tiniest quantum of electromagnetic radiation. It can also be understood as the basic unit of all light that exists around us. 


Photons are never static. In a vacuum, they move at a constant speed, which is the speed of light (2.9 × 108 m/s). The speed of light is represented by ‘c’. 


According to Einstein, the energy possessed by an electron is equal to the product of its frequency and Planck’s constant. He proved that light is nothing but a flow of electrons. More the number of photons present in a beam of light, greater will be its intensity. He experimentally explained that photons have a dual nature, they can behave both as particles and waves. The main postulate of his theory was that the energy of light is related to its frequency. With the help of his experiments on Photoelectric effect, he was able to derive the value of Planck’s constant which came out to be 6.6 × 10-34 kgm2/s, exactly what Planck had calculated in 1900 through his work on electromagnetic waves. 


The energy and momentum of a photon are dependent on its frequency and wavelength, by the equation 


E =hc/λ


The important characteristics of photons are as follows:

  1. Photons possess no mass or rest energy. They are only existent as particles in motion. 

  2. Despite having no rest mass, they are considered as elementary particles. 

  3. Photons do not have any charge. 

  4. They are quite stable.

  5. Photons are carriers of energy and momentum, depending on the frequency. 

  6. They can interact with other subatomic particles such as electrons. 

  7. Photons can be created or destroyed by various natural phenomena, such as absorption or emission of radiation. 

  8. They travel with the speed of light in vacuum. 


What is the Difference Between Photons And Electrons?

Photons 

Electrons

They are massless. 

They have a negligible mass. 

They are neutral. 

They have a negative charge.

Photons constitute electromagnetic radiation.

Electrons constitute electricity.

Its speed in vacuum will always be equal to the speed of light.

Its speed can be zero or anything lesser than the speed of light.

It has a spin of 1.

It has a spin of ½.


Did You Know?

  1. Not just light, all electromagnetic radiation is composed of photons. 

  2. Einstein conceptualized the idea of photons, but the term ‘photon’ was first used by Gilbert Lewis. 

  3. A photon can be created or destroyed, but it never decays on its own.

FAQ (Frequently Asked Questions)

Question 1: How can a photon be formed from an electron?

Solution: Every electron is naturally present in a shell. But, if it is given some energy, it absorbs it and moves to a higher energy level. When this electron (in a higher shell) makes its way back to its original shell, the energy absorbed by it is emitted in the form of a photon (a packet of energy). The characteristics of this photon are very specific. It has a frequency (colour) that matches the distance the electron falls. In the reverse process, when a photon interacts with an atom, it transfers its energy to the electron (externally absorbed energy), gets in an excited state and moves to a higher energy level.

(image will be uploaded soon)

Question 2: What is Meant by the dual nature of light?

Solution: The dual nature of light is used to represent the fact that it can behave both as a particle and a wave. Einstein, through his photoelectric experiment, proved that light behaves as a particle. He showed that a beam of light is capable of ejecting electrons from the surface of the metal. Contrarily, Thomas Young performed a double-slit experiment to prove that light behaves as an electromagnetic radiation. In this experiment, when the light was passed through a pair of parallel slits, it formed dark and light bands. Quantum mechanics explains that light has a dual nature. It can act both as a wave or a packet depending on the conditions. 

(image will be uploaded soon)


(image will be uploaded soon)