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Electromagnetic induction, which is sometimes also called magnetic induction, is related to emf or electromotive force across an electric conductor. At the same time, there is a change occurring in the magnetic field.

Michael Faraday is the one who discovered induction for the first time in 1831 when James Clerk, who was a Scottish mathematician, described Faraday’s law of induction mathematically.

Faraday’s laws of electromagnetic induction are the basis of electromagnetism. It predicts how a magnetic field will interact with an electric circuit for the production of electromotive force (emf). The whole thing combined is called electromagnetic induction.

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Electromagnetic Induction: 

It is the phenomenon of the production of induced current in a coil placed in a region where the magnetic field changes with time.

  • Fleming’s right-hand rule gives the direction of the induced current.

To derive the laws of electromagnetic induction, Michael Faraday performed many experiments. His three experiments amongst all are the most important ones in discovering electromagnetic induction.

Michael Faraday has given two laws of electromagnetic induction.

Faraday’s first law of electromagnetic induction :

In his first law of electromagnetic induction, Faraday and Henry worked together. It is the first conclusion made by Faraday after his many experiments. Thus, we can estate the first law of Faraday regarding electromagnetic induction as follows:

An electromotive force (emf ) is generated when a current is induced in a conductor circuit, creating a magnetic field variation.

The current induced in a circuit is termed as induced current when the conductor circuit is closed. 

We can change the magnetic field intensity in a closed-loop in different ways. Let us discuss some of them below :

  • A change in the magnetic flux can be brought
  • A change in the magnetic flux can also be obtained by moving the coil into the magnetic field.
  • Getting the coil out of the magnetic field can also change the magnetic flux.
  • We can also change the area of the coil which is placed in the magnetic field.
  • We can move the magnet towards the coil to change the magnetic flux.
  • Moving the magnet away from the coil can also change the magnetic flux.

Faraday’s second law of electromagnetic induction:

According to Faraday’s second law of electromagnetic induction, the emf or electromotive force generated by the change in the magnetic field in the coil is equal to the rate of the change of the flux leakage.

Methods to increase the induced electromotive force in a coil:

  • The induced electromotive force will increase if we increase the number of turns in a coil.
  • If we expand the strength of the magnetic field, the electromotive force will increase.
  • If we increase the speed of relative motion between the coil and the magnet, the electromotive force will increase.

Application of Faraday’s laws

  • Faraday’s laws of electromagnetic induction are used in musical instruments such as guitar, violin etc., operated by electricity.
  • The basic principle on which an electric generator works is Faraday’s law of mutual induction.
  • Power transformers work on Faraday’s laws of electromagnetic induction.
  • The induction cookers used for cooking also work on the principles of Faraday’s law of electromagnetic induction.
  • Maxwell’s equations use the converse of Faraday’s laws of electromagnetic induction.
  • Electromagnetic flowmeter works on the principles of Faraday’s laws which is used to measure the velocity of the fluids. 

Conclusion

Michael Faraday was an English scientist of the 19th century. He is credited with many great discoveries in physics and chemistry. However, he is popularly known for his discovery in the field of electromagnetism. Where he experimented with a coil and a magnet. Faraday performed several experiments to give the law on electromagnetic induction. The term induction means to generate or induce something. He has passed two electromagnetic laws of induction. He was the first who introduced electromagnetic induction to us. The term electromagnetic induction refers to the production of electric currents caused by the magnetic field. A magnetic field produces a current in a conductor. His law is related to the show of electromotive force. An electromotive force may be an electrical action made by a non-electrical source. It is abbreviated as emf. The transducers provide electromotive force by converting a form of energy to another form of energy, such as a transducer battery, which converts chemical energy to electrical energy.

 Faraday’s law of induction is the basic operating principle of inductions, electric generators, electric motors, power transformers, musical instruments such as electric guitar, electric violins etc. Thus, we can say that the law of induction given by Faraday is beneficial in our daily life as we deal with so many electric types of equipment of our everyday use, which are working in Faraday’s laws of electromagnetic induction. 

Factors affecting the mean free path

The factors on which the mean free path depends are:-

  1. Diameter of a molecule (inversely proportional to the square of diameter)
  2. Number of gas molecules per unit. (inversely proportional to number of gas molecules)
  3. Indirectly depends on factors like temperature( directly proportional), pressure (inversely proportional) and Boltzmann constant.
  4. When density increases, it causes more collisions, resulting in a decrease in the mean free path.

Specific mean free path:

The mean free path that is independent of density is called a specific mean free path. This doesn’t change with the change of density with respect to time.

The unit of specific mean free path is g/cm²

To obtain the actual mean free path, the specific mean free path can be divided by the density.

Use of Mean Free Path in different fields :

  1. Radiography :

    In gamma-radiography, the mean free path of a pencil beam of mono-energetic photons is the average distance a photon travels between collisions with the atoms of the target material.

    In X-ray radiography, the photons are not mono-energetic, and hence, the calculation of the mean free path becomes very complex. However, the photons follow a spectrum of distribution of energies and hence, when they move through the target material, they are attenuated with probabilities with respect to their energies. This results in the hardening of the spectrum because of which the mean free path of the spectrum changes with distance.

  2. Electronics :

    The mean free path of a charge carrier in a metal L is proportional to the electric mobility. The thickness of a thin film can be lesser than the mean free path, making surface scattering much more noticeable and increasing resistivity.

  3. Acoustics:

    The relation for the mean free path of a single particle that bounces off the walls helps in the derivation of the Sabine equation in acoustics. The derivation uses the geometrical approximation of sound propagation.

  4. In Nuclear and Particle Physics:

    In nuclear and particle physics, the concept of mean free path is replaced by the concept of attenuation length. For high-energy photons interacting by  electron-positron pair production, the concept of radiation length is used in place of the concept of mean free path.

    1. In transverse processes like viscosity, heat conduction, diffusion and electrical conduction, the process of calculations requires the use of the concept of mean free path.
    2. In many cases, particles whose motion and interaction conform to the laws of quantum mechanics, the concept of mean free path is used in calculations. In such cases, the calculations with the mean free path become extremely complex.

Important points to remember

  • The free path between two successive collisions is a straight line with constant velocity as until collisions.
  •  After collision, they follow zigzag trajectories of different lengths. These zigzag trajectories are called molecular free paths, and the average of their varying length is referred to as mean free path.
  • This zigzag trajectory is an example of diffusive motion (diffusion) or can also be compared with a random walk.
  • The momentum and energy remain constant in these collisions, and hence ideal gas laws are always valid.
  • There’s a need to quantify the mean free path since its measurement and the characterisation of randomly moving gas molecules are very different.
  • The more collisions there are, the less is the mean free path.

Conclusion

When the particles pass through any material, they may start moving in different directions due to the collisions that take place in between them. The average distance between the particles after collision is known as the mean free path, which depends on factors like pressure, volume, temperature, density, etc. It also depends on the type of cross-section used in the calculations, i.e. scattering cross-sections or total cross-sections. It also depends upon the energy distribution of the particles with respect to the medium.