What is magnetism?

Magnetism is an important term in physics that helps you learn about one of nature's most basic interactions: the interaction between moving charges. The magnetic force is a distance interaction similar to the gravitational and electrostatic forces. We have learned about Electrostatic fields and forces. When charges move it constitutes the current in a circuit. The movement of charges is known as Electric Current. These moving electric charges produce field and forces. But have you ever considered the possibility of a connection between electricity and magnetism? In 1820, Oersted discovered such a correlation. We now understand how closely magnetism and electricity are related.

Magnetic Field

Magnetic fields, including gravitational fields, are invisible and unquantifiable. We get a feeling of the gravitational force of the Earth's field on ourselves and the objects around us, but we don't feel the same with magnetic fields. We know magnetic fields exist because of their effect on magnetized metal parts, naturally magnetic rocks like lodestone, and temporary magnets.

Greeks were aware of the phenomena of magnetism as far back as 600 B.C. They discovered that magnetite (Fe₃O₄) stones attracted iron particles. Natural magnets are naturally occurring magnetite fragments. While natural magnets are weak materials such as iron, nickel, and cobalt can be transformed into powerful permanent magnets. Human and artificial magnets have the same properties. Both magnets, whether natural or man-made, have the same properties.

1.Directive Property: When a small bar magnet is suspended freely on its center of mass and rotated around a vertical axis, it always rotates in a north-south direction.

2.A magnet's attractive property is that it attracts small magnetic materials such as iron, nickel, and cobalt. The force of attraction is strongest near the magnet's ends. The magnet's poles are these points. The pole that points to the geographic north is referred to as the north pole, and the pole that points to the geographic south is referred to as the south pole in a freely suspended magnet. Do our earth's directive and attractive properties imply that it also functions as a magnet? Yes, it is.

Earth's magnetic field can be fully in the context of three basic quantities known as earth's magnetic field elements:

• Inclination angle
• Declination angle
• The horizontal portion of the earth's field

3.The opposite poles of two magnets attract each other, while the like poles repel each other.

4.A magnet's poles are inseparable, so the simplest specimen that generates a magnetic dipole is the result of a magnetic field.

5.When a magnet is brought close to a piece of iron, the closer end acquires opposite polarity, while the farther end acquires the same polarity. Magnetic induction is the term for this phenomenon.

Magnetic Field Lines

Drawing the field lines is a very useful way to picture the position and magnitude of a field.

• At any point, the tangent to the field line decides the direction of magnetic field vector B.
• The magnetic field's intensity in a region is proportional to the number of field lines that pass through a surface's unit area. kept perpendicular to the lines. As a result, when the field lines are closer together, the magnetic field B is higher, and when they are further apart, the magnetic field B is smaller.

Magnetic Flux

The total number of magnetic field lines passing through a given area is referred as the magnetic flux. Magnetic flux gives the total amount of magnetic field in a particular area. The area under consideration can be altered in terms of size or orientation ﴾with the magnetic field﴿. If we use a simple flat surface with area A as our test area and there is an angle formed by the surface's normal and a magnetic field vector (magnitude B), we can calculate the magnetic flux.

Φ=BAcosθ

Where,

• Φ is the magnetic flux
• B is the magnetic field
• A is the area
• θ the angle at which the field lines pass through the given surface area

Magnetic Flux Unit

A flux metre is used to calculate magnetic flux. The following are the SI and CGS units of magnetic flux:

• Weber is the SI unit for magnetic flux (Wb).
• Volt-seconds are the fundamental unit.
• Maxwell is the CGS unit.

The angle is zero when the field is perpendicular to the surface, and the magnetic flux is simply B A. Following figure depicts a flat test area exposed to a magnetic field at two different angles, as well as the resulting magnetic flux.

Magnetic Flux Density

The force acting per unit current per unit length on a wire placed at right angles to the magnetic field is known as magnetic flux density (B).

• Units of B is Tesla (T) or kgs^-2A^-1
• B is a vector quantity

B=F/Il  

Where, l=length of wire F=total force acting on the wire I=current flowing through the wire.

Magnetic Force

The magnetic force is generated by the motion of charges and is a consequence of the electromagnetic force, one of the four fundamental forces of nature. Between two objects containing charges moving in the same direction, there is a magnetic attraction force. A repulsive force exists between objects with opposite charges traveling in opposite directions.

The Lorentz Force Law describes the magnetic force.

$\overrightarrow{F}=\overrightarrow{q}(\overrightarrow{v}\times \overrightarrow{B})$ i.e., using the vector cross product

The magnitude of the force is F,   F=qvBsinθ

The right-hand-slap rule can be used to determine the force's direction. The path of the force is defined by this rule as a ‘slap' of an open hand.

Coulomb’s Law

The force of interaction acting between two magnetic poles is directly proportional to the product of their pole strengths and inversely proportional to the square of the distance between them.

where m₁, m₂ = pole strengths, r = distance between poles and μ_o = permeability of free space.

Magnetic Dipole

A magnetic dipole is an arrangement of two unlike magnetic poles separated by a very small distance, for example, a small bar magnet, a magnetic needle, or a current-carrying loop.

Magnetic Dipole Moment

The magnetic dipole moment can be defined corresponding to electric dipole moment. It is obtained by multiplying the distance (2 l) between the two poles and the pole strength (m) of either pole of the magnet.

Moment of magnetic dipole M = m (2 l)

Its SI unit is ‘joule/tesla’ or ‘ampere-metre²‘.

It travels from the south pole to the north pole.

Electromagnetism

André-Marie Ampère 20 January 1775 – 10 June 1836 was a French physicist and mathematician who was one of the pioneers of classical electromagnetism, which he referred to as "electrodynamics."

Magnetism in Matter

Based on their behavior in a magnetic field, we can divide materials into three categories.

• Diamagnetic materials are feebly repelled by a magnet.
• Paramagnetic materials are feebly attracted by a magnet.
• Ferromagnetic materials are very strongly attracted by a magnet.

Diamagnetism: A magnetic field repels diamagnetic materials because it induces a magnetic field that is generated in them in the opposite direction, resulting in a repulsive force. Mercury, water, iron, bismuth, and gold are examples of diamagnetic materials.

Paramagnetic: An externally applied magnetic field attracts certain materials weakly, causing internal, induced magnetic fields in the direction of the applied magnetic field, which is known as paramagnetism. Examples of paramagnetic materials are Magnesium, lithium, molybdenum, etc

Ferromagnetic: Ferromagnetism is the fundamental process by which certain materials (such as iron) form permanent magnets or are attracted to magnets. Examples of ferromagnetic materials are iron, cobalt, and nickel, etc.

Common Mistakes

• Keep in mind that a moving point charge does not produce a steady magnetic field. To apply the laws of magnetostatics, we must assume existing distributions.
• When dealing with multiple point charges, we must be very careful to add up their contributing electric fields as vectors, or we will never get a fair (and correct) result.

Context and Applications

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for

• 10th,11th,12th Standard.
• Engineering Students.
• This is a term that is commonly used in industry and modern technology.
• Many electrical and electromechanical devices, such as electromagnets, electric motors, generators, transformers, and magnetic storage, are built on this foundation (e.g., tape recorders and hard disks).

Related Concepts

• Magnetic Susceptibility
• Domains of Magnetic Substance
• Hysteresis in Magnetic materials