Courses
Courses for Kids
Free study material
Offline Centres
More
Store Icon
Store

Faraday Effect

Reviewed by:
ffImage
hightlight icon
highlight icon
highlight icon
share icon
copy icon
SearchIcon

Faraday Rotation Effect

In 1945, an English scientist Michael Faraday FRS observed an effect while examining the effect of magnetic field on plane-polarized light waves. This effect was named after him as the Faraday Effect.

Faraday Effect is also known as the Faraday Rotation or the Magneto Optical Faraday Effect.

Faraday Effect causes the rotation of the plane of polarization (plane of vibration) of electromagnetic waves in particular substances in a magnetic field. 

This rotation varies proportionally with the projection of the magnetic field along the direction of the propagation of light.

This page discusses the observations of the Faraday effect, along with the Faraday Tyndall effect, and the Faraday effect in Layman's terms.


Faraday Effect

The Faraday effect is a physical magneto optical Faraday Effect MOFE) phenomenon.

The Faraday effect results in a polarization rotation that varies proportionally with the projection of the magnetic field along the direction of the light propagation. 

Do You Know?

Faraday Effect is a special case of gyro-electromagnetism. 

The gyro-electromagnetism is achieved only when the dielectric permittivity tensor is diagonal.


History of Faraday Effect

The Faraday effect discovered this effect in 1845. It was the first experimental evidence that light and electromagnetism relate to each other.

James Clerk Maxwell completed the theoretical basis of electromagnetic radiation (including visible light) in the 1860s and 1870s and Oliver Heaviside. 

For most of the part, this effect occurs in optically transparent dielectric materials like liquids under the influence of magnetic fields.

The left and right circularly polarized waves propagating at varying speeds lead to Faraday. 

Therefore, the property of propagation is known as circular birefringence. 

As a result, linear polarization can decompose into the superposition of two equal-amplitude circularly polarized components of opposite handedness and different phases. 

Therefore, the Faraday effect induces the effect of a relative phase shift that rotates the orientation of a wave's linear polarization.


Faraday Tyndall Effect

In the mid-1850s, Faraday spent an ample amount of time investigating the properties of light and matter. 

He made several hundred gold slides (thin enough to be transparent). These gold leaves were made by hammering the metal into very thin sheets (which were too thick for his purpose).

Also, he examined these thin sheets by shining light through them. However, Faraday used chemical means rather than mechanical.

For most of the part, his process involved washing the films of gold, which Faraday noticed produced a light/fainted ruby coloured fluid. 


[Image will be uploaded soon]

                                       

Further, he kept fluid samples in bottles to use for future experiments: shining a beam of light through the liquid. 

In his record, Faraday observes that the cone was well-defined in the fluid by the illuminated particles.

As a result of this experiment, Faraday is known as one of the first researchers into nanoscience and nanotechnology.

Thus he realized that this cone effect was made because the fluid contained suspended gold particles that were too small to be observed with the scientific apparatus of the time, moreover,  which scattered the light to the side. This is known as the Faraday Tyndall effect in colloids.


Inverse Faraday Effect

The orbit of an electron directed by a circularly polarized light beam is usually a solenoid with an axis parallel to its displaced initial velocity

As a rule, the motion of the electron produces a solenoidal current that generates a magnetic moment depending on the direction of the shifted initial velocity.

The average of magnetic moments per unit volume in a free electron gas gives a plain microscopic explanation for the theory of the inverse Faraday effect in metals.


Inverse Faraday Effect in Optics

In optics, the inverse Faraday effect is the inverse of the Faraday effect. 

A static magnetization M(0) induces by an external vibrating electrical field with the frequency ω.  Here,  ω can be obtained with a high-intensity laser pulse.

Here, the induced magnetization lies proportionally to the vector product of E and E*.

M (0) α E (ω) and E* (ω)

From this equation, we see that the circularly polarized light with the frequency should induce a magnetization along with the wave vector k. 

Because \[\overrightarrow{E}\] is in the vector product. Also, left- and right-handed polarization waves should induce magnetization of opposite signs.

Thus the induced magnetization is comparable to the saturated magnetization of the media.


Magneto Optical Faraday Effect

In physics, the Faraday effect, the Faraday rotation effect or the magneto optical Faraday effect are synonyms. To be simply speaking, the Faraday effect is the magneto optical phenomenon. 

A Faraday effect or the magneto optical phenomenon is the interaction between light and a medium. We refer to this phenomenon as the magneto optic Faraday Effect or MOFE.


Faraday Cage Effect

A Faraday cage a.k.a Faraday shield. It is a mesh or metallic enclosure that blocks electromagnetic fields. 

A Faraday shield is formed by a continuous covering of conductive material. 

In the case of a Faraday cage, a cage can be formed by a mesh of such conductive materials.

The Faraday cage works on the principle of an external electrical field that causes electrical charges to reside within the cage’s conducting material distributed so that they cancel the field's effect in the cage's interior.

Faraday cages protect sensitive electronic equipment from external RFI or the radio frequency interference.

They also consider devices that produce RFI, likewise radio transmitters, to prevent their radio waves from interfering with other nearby devices.

They also protect people and equipment against electric currents such as lightning strikes and electrostatic discharges.


[Image will be uploaded soon]       

                                     

As a result, the enclosing cage conducts current around the outside of the enclosed space and nothing passes through the interior.


Faraday Effect in Layman's Terms

A dipole moment (usually just called "magnetic moment") is something an object has that creates it and behaves sort of like a compass needle. 

It's kind of a virtual compass needle enclosed within an object. 

When the thing is placed during a magnetic flux, the thing rotates until its dipole moment is lined up with the magnetic flux. 

The dipole moment of a compass needle itself is, of course, parallel to the length of the needle; so is that of a magnet. 

A flat loop of wire with a circulating current also features a dipole moment, which is perpendicular to the loop; so once you place the loop during a magnetic flux, it'll tend to rotate until it's perpendicular to the sector (because then the moment of a magnet are going to be parallel to the field).

FAQs on Faraday Effect

1. What is the Faraday Effect, and why is it important in Physics?

The Faraday Effect is the rotation of the plane of polarization of light as it passes through certain materials under the influence of a magnetic field aligned with the direction of light propagation. This effect was the first experimental evidence that light and electromagnetism are linked, helping to lay the foundation for modern electromagnetic theory as per the CBSE Physics syllabus.

2. How does the Faraday Effect demonstrate the relationship between light and a magnetic field?

When a beam of plane-polarized light passes through a transparent medium in the presence of a magnetic field along its propagation direction, the plane of polarization rotates. The angle of rotation is directly proportional to the magnetic field strength and the path length through the material, illustrating the interaction between electromagnetic waves and magnetic forces.

3. Can you explain the concept of Faraday Rotation using real-world examples?

The Faraday Rotation is observed in devices like optical isolators and modulators used in fiber optic communications. For example:

  • In astronomy, it helps study magnetic fields in interstellar space by analyzing polarized light from distant galaxies.
  • It is also used to protect lasers from back reflections in scientific instruments.

4. What is the difference between the Faraday Effect and the Tyndall Effect?

The Faraday Effect refers to the rotation of light's polarization due to a magnetic field, while the Tyndall Effect involves the scattering of light by tiny particles suspended in a colloid. The Faraday Tyndall effect occurs when Faraday observed coloidal gold particles causing scattered light, demonstrating both concepts together.

5. What determines the magnitude of rotation in the Faraday Effect for a material?

The magnitude of rotation in the Faraday Effect depends on:

  • Strength of the external magnetic field
  • Path length through which light travels
  • Type of material (its Verdet constant)
  • Wavelength of the incident light

6. Why are optically transparent dielectric materials commonly used to study the Faraday Effect?

Optically transparent dielectrics allow light to propagate with minimal absorption, making it easy to observe the rotation of polarization without significant loss of intensity. Their physical properties, such as molecular structure and Verdet constant, also significantly influence the degree of rotation.

7. How did Michael Faraday discover the effect and what was its historical significance?

Michael Faraday discovered this effect in 1845 by passing polarized light through glass in a magnetic field and observing the plane of polarization rotated. This experiment provided direct evidence that magnetism can influence light, linking optical and electromagnetic phenomena, and paved the way for Maxwell's equations.

8. What misconceptions do students commonly have about the Faraday Effect?

Common misconceptions include:

  • Believing the effect occurs in all materials, rather than specific magneto-optic substances.
  • Assuming any direction of magnetic field affects the polarization; in reality, only the component along the light's path causes rotation.
  • Confusing the Faraday Effect with simple magnetic deflection or interference, which are distinct phenomena.

9. What is the inverse Faraday Effect and how does it contrast with the regular Faraday Effect?

The inverse Faraday Effect is when a magnetic moment is induced in a material by a circularly polarized electromagnetic wave, compared to the regular Faraday Effect where a magnetic field affects light's polarization. Essentially, the cause and effect are reversed.

10. How does the Faraday Cage relate to Faraday's research, and what are its modern applications?

A Faraday Cage (Faraday Shield) is a conductive enclosure that blocks external static and non-static electric fields. Its working principle is based on redistribution of charges, so the internal region is shielded from external fields. Modern applications include protecting sensitive electronic devices from radio frequency interference, and safety from lightning strikes.

11. Why is understanding the Faraday Effect important for CBSE board exams in Physics?

The Faraday Effect is a frequently examined concept relating electromagnetic theory, optics, and applications in technology. Grasping its definition, experimental method, and real-world relevance helps in answering both theory and application-based questions for the Physics examination as per CBSE 2025–26.

12. How is the Faraday Effect mathematically represented?

The angle of rotation (θ) produced by the Faraday Effect is given by the formula: θ = VBL, where V is the Verdet constant of the material, B is the magnetic field strength, and L is the length of the material through which light passes. This relationship quantifies the rotational effect on polarized light.