What are Natural Magnets?

A magnet is a material that has the ability to exert a detectable force on other materials without actually coming into contact with them. A magnetic force attracts or repels objects. While all known materials have a magnetic force, it is so minimal in most that it is barely detectable. The magnetic force is substantially stronger in other materials, which are referred to as magnets. The Earth is a massive magnet in and of itself.

Properties and Characteristics of Natural Magnets

Every magnet has two points of highest magnetic force. The poles are defined as these two points. These poles would be at the opposing ends of a rectangular or cylindrical bar magnet. The north-seeking pole is known as the north pole, and the south-seeking pole is known as the south pole.

Properties of Magnets

• When a magnet is dipped in iron filings, the iron chips are attracted to the magnet's ends, where the attraction is strongest. The poles of magnets are at the opposite ends and are the part of the magnet with the strongest magnetic field.
• When suspended in mid-air, a magnet always points north-south. The geographical north pole is to the north, and the geographic south pole is to the south.
• When the distance between the two magnets is smaller, the magnetic force between them is larger.
• Poles that are similar repel one another, but poles that are dissimilar attract one another.
• Magnetic poles are always found in pairs.

Characteristics of Magnets

• Suspending the magnet in mid-air aids in determining which poles of the magnet are north and south.
• The law of magnetic poles states that like poles repel and dissimilar poles attract.
• When a magnet is cut into two pieces, both pieces will have a north pole and a south pole.
• The sure magnetization test is used to determine whether or not a certain rod is magnetized by measuring the attraction or repulsion of the iron rod and magnet.

Magnetostatic Equation of Natural Magnets

Magnetostatics is a concept that is used to determine the magnetic field by using an approximation of Maxwell's equation. The equations of magnetostatics begin with Gauss' magnetic law in free space:

$\nabla ·\mathrm{B}=0$

The above equation suggest that the magnetic field around a closed surface is zero.

Maxwell–Ampère's law (static version) states that the magnetic flux density is directly proportional to the current density in the vacuum.

$\nabla ·\mathrm{B}={\mathrm{\mu }}_0\mathrm{J}$

Here, $\mathrm{B}$ is the magnetic flux density, $\mathrm{J}$ is current density, and ${\mathrm{\mu }}_0$ is vacuum permeability constant.

Types of Magnets

• Permanent magnet
• Temporary magnet
• Electromagnet

Permanent Magnets

Permanent magnets are the most often utilized magnets. These are called permanent magnets because once magnetized, these magnet don't lose their magnetic properties. A permanent magnet is a magnetized item that generates its own magnetic field. A refrigerator magnet, which is used to keep notes on a refrigerator door, is a daily example.

Permanent magnets exert a force on objects that is independent of external forces. Lodestone, or iron ore magnetite, is a naturally occurring permanent magnet. Other permanent magnets can be made by applying a magnetic force to certain materials. These materials keep their magnetic characteristics when the force is withdrawn. Although the magnetic characteristics of these materials may vary over time or at high temperatures, they are commonly thought to be permanently magnetized, thus the term.

Permanent magnets are composed of rare-earth metal alloys and minerals such as lodestone, as well as specific alloys (ferromagnetic materials) such as iron, nickel, and cobalt.

Types of Permanent Magnets

• Alnico
• Ceramic or ferrite
• Samarium Cobalt (SmCo)
• Neodymium Iron Boron (NIB)

Despite their name, it is possible for permanent magnets to be demagnetized in certain ways:

• Magnets are subjected to severe temperatures.
• When the magnet's atoms are pounded, the magnetic attraction between them weakens.
• Inadvertently striking one magnet with the other reduces the magnetic strength.

Temporary Magnets

When a nonmagnetic material is magnetized in the presence of a magnetic material, the magnet so formed is called a temporary magnet. These materials lose their magnetic properties when the magnetic field is removed. Temporary magnets include iron nails and paper clips.

Electromagnets

Electromagnets are formed out of a wire coil wrapped around an iron-based metal core. When this material is exposed to an electric current, a magnetic field is produced, causing it to behave like a magnet. The electric current can be used to modulate the strength of the magnetic field.

Electromagnets are a type of magnet. They are manufactured by wrapping a coil of wire around specified materials. These materials produce a magnetic force when an electric current is fed through the coil. When the current is turned off, the magnetic force of these materials approaches zero. Without an electric current flowing through the coil, electromagnetic materials retain little, if any, magnetic characteristics.

Electromagnets are most often made of pure iron and iron alloys. Low-frequency power transformers use silicon iron and carefully processed iron-cobalt alloys.

Lines of Force Around an Electromagnet

The magnetic field produced by an electromagnet is stretched out in the shape of a bar magnet, resulting in a distinct north and south pole, with the flux proportional to the amount of current running in the coil. The magnetic field intensity will be raised if more layers of wire are coiled onto the same coil with the same current flowing.

The quantity of flux accessible in any particular magnetic circuit is related to the current running through it and the number of wire turns within the coil. This relationship is known as Magneto Motive Force, or MMF, and it is described as follows:

Magneto Motive Force (MMF)=$\text{I×N }$Ampere Turns

A current, I, flowing through a coil of N turns is the magneto motive force. The ampere turns of the coil define the magnetic field intensity of an electromagnet; the more wire turns in the coil, the stronger the magnetic field.

Magnetic Field Strength for Electromagnets

The strength of this field around the conductor is related to its distance from it, with the strongest point being closest to the conductor and decreasing when far away. The intensity of the field is governed by the current flowing and the distance from it in the case of a single straight conductor.

The method for estimating a long straight current carrying conductor's "Magnetic Field Strength," H, also known as "Magnetizing Force," is obtained from the current flowing through it and the distance from it.

For a coil of wire:

$\mathrm{H}=\frac{\mathrm{I}\times \mathrm{N}}{\mathrm{L}}$

For straight donductor:

$\mathrm{H}=\frac{\mathrm{I}}{2\mathrm{\pi r}}$

Here,

• H is the strength of the magnetic field in ampere-turns/meter, A/m
• N is the number of turns of the coil
• I is the current flowing through the coil in amps, A
• L is the length of the coil in meters, m

Context and Applications

There are any applications of natural magnets in:

• Compasses
• Electric motors
• Microwave ovens
• Coin-operated vending machines
• Light meters for photography
• Automobile horns
• Televisions
• Loudspeakers
• Tape recorders

Practice Problems

1. What are the types of magnets?

a. Permanent magnets
b. Temporary magnets
c. Electromagnets
d. All of the above

Answer: d

Explanation: The types of magnets are permanent magnets, temporary magnets, and electromagnets.

2. Which of the following is a type of permanent magnet?

a. Alnico
b. Ceramic or ferrite
c. Samarium Cobalt (SmCo)
d. Neodymium Iron Boron (NIB)
e. All of the above

Answer: e

Explanation: The types of permanent magnets are alnico, ceramic or ferrite, samarium cobalt (SmCo), neodymium iron boron (NIB).

3. When the distance between the two magnets is __________, the magnetic force between them is larger.

a. Smaller
b. Larger
c. High
d. None

Answer: a

Explanation: When the distance between the two magnets is smaller, the magnetic force between them is larger.

4. The law of magnetic poles states that like poles ______ and unlike poles attract.

a. Attract
b. Like
c. Repel
d. None

Answer: c

Explanation: The law of magnetic poles states that like poles repel and dissimilar poles attract.

5. ___________ lose their magnetic properties when the magnetic field is removed.

a. Permanent magnets
b. Temporary magnets
c. Electromagnets
d. All of the above

Answer: b

Explanation: Temporary magnets lose their magnetic properties when the magnetic field is removed.