[Physics Class Notes] on Electrons and Photons Pdf for Exam

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?

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.