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The magnetic field is the zone in which the force of magnetism works around a magnetic substance or a moving electric charge.
Magnetic forces can be observed in a magnetic field, a vector field near a magnet, an electric current or an electric field that is changing. Moving electric charges and inherent magnetic moments of primary particles, connected with a fundamental quantum feature known as spin, combine to generate a magnetic field. Both magnetic and electric fields are components of electromagnetic force, one of nature’s four fundamental forces.
Properties of Magnetic Field Lines
- Magnetic field lines are never overlapping.
- The density of the field lines determines the field’s strength.
- Magnetic field lines always form closed loops.
- Magnetic field lines always originate at the north pole and end at the south pole.
Magnetic Susceptibility
The magnetic susceptibility of a substance is a measure of its magnetism in an applied magnetic field. It is the ratio of the applied magnetising field intensity H to the magnetisation M (magnetic moment per unit volume). It is denoted by the symbol ‘ χ’. This can be classified into two categories:
- Paramagnetism is an alignment with the magnetic field that is greater than zero,
( χ > 0).
- Diamagnetism is an alignment with the magnetic field that is less than zero,
(χ < 0).
Diamagnetic Material
Diamagnetic materials can be defined as the material that repels the magnetic field, as it induces a magnetic field in the opposite direction.
Diamagnetism is observed in all materials and it is one of the weakest forces.
A few of the examples of diamagnetic material are wood, water and most organic compounds, such as petroleum and some plastics and a few other metals, such as copper, mercury and gold.
Organic materials such as living cells also have diamagnetic properties, although they are weakly diamagnetic.
Superconductors
Superconductors are the ideal diamagnets because they follow the Meissner effect, which causes the superconductors to eject all magnetic fields.
Levitation and Magnetic Field
A diamagnetic material may be levitated without power in a stable equilibrium magnetic field. Earnshaw’s theorem appears to rule out static magnetic levitation as a possibility. It only applies to positive susceptibilities, such as ferromagnets (which have a permanent positive moment) and paramagnets (which induce a positive moment). Field maxima, which do not exist in free space, attract these species. Because field minima attract diamagnets (which create a negative moment), they can exist in free space.When a thin slice of pyrolytic graphite is exposed to a magnetic field, the slice of pyrolytic graphite begins to levitate.
Frog in the Magnetic Field
A weak diamagnetic property exists in the living cell. Therefore, when a frog is subjected to a magnetic field, the frog starts to levitate due to the diamagnetic property in the living cell.
Similarly, NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, revealed in September 2009 that it has successfully levitated mice using a superconducting magnet, which was a significant step forward because mice are physiologically closer to humans than frogs.
Theory of Levitation
Electrons settle into orbitals with virtually little resistance in most materials, forming current loops. Because, similar to superconductors, which are practically perfect diamagnets, any applied magnetic field would create currents in these loops that would oppose the change. Many materials display diamagnetism yet respond very little to applied fields because electrons are severely imprisoned in orbitals by the charge of the protons and further confined by the Pauli exclusion principle.
The Bohr–Van Leeuwen theorem states that neither diamagnetism nor paramagnetism can exist in a perfectly classical system. In contrast, the classical Langevin theory of diamagnetism makes the exact prediction as to the quantum theory.
Conclusion
The magnetic field is where the force of magnetism works around a magnetic substance or a moving electric charge. Diamagnetic materials can be defined as the material that repels the magnetic field. When a frog is subjected to a magnetic field, the frog starts to levitate due to the diamagnetic property in the living cell.
