Magnetism – Definition, Cause, Theory and Components

A magnet is an object that produces magnetic fields to attract unlike poles and repel like poles. They work on the idea of electromagnetic force which is capable of attracting and repelling. In the case of the gravitational force, it only attracts.

The electromagnetic force remains stronger compared to it but. Magnetism on the other hand refers to the interaction between moving charges and is interaction at distance.

The concept of magnetism works under the magnetic field. This field is not tangent but the pull can be felt. It is there just like the concept of gravity.

Though we don’t come in direct contact with it, it is visible in magnetized metal and rock objects. Certain observations like copper coils, magnetic needles, and more led to the discovery of magnetic fields. The nuclear force is stronger than EM but has a lower range.

The magnetic field reduces with distance from the conductor in a current. The right thumb rule helps us to figure out the magnetic field direction due to the conductor. Let us learn about magnetism in more detail now.

Properties of Magnet

• The poles of the magnet are present at the end of these. This is why iron filings stick to the magnet end and hang there.
• The magnetic poles are always present in a pair.
• A magnet in free air points in the north and south direction. The north pole points towards the geographic north and the south pole directs towards the geographic south.
• The magnetic like poles repel while the unlike poles always attract.
• The magnetic force is more when the distance is less between them.

Types of Magnets

There are mainly three types of magnets. They are –

1. Permanent magnet
2. Temporary magnet
3. Electromagnets

Permanent Magnet

These are the most common magnets. They are permanent because they remain magnetic or have magnetic property forever after getting magnetized. The only way to demagnetize them is to expose them to extreme temperatures.

This makes magnetic atoms lose their magnetic property. Hammering them will reduce their strength.

There are four types of permanent magnets –

• Ceramic or ferrite
• Alnico
• Samarium Cobalt
• Neodymium Iron Boron

Temporary Magnet

These magnets only possess magnetic properties when present inside the magnetic field. This means they lose their property after getting out of the field. This is the reason why they are temporary magnets. Iron nails and paper clips come under this division of magnets.

Electromagnets

This kind of magnet has an iron metal core wrapped in a coil of wire. They possess magic property in the presence of electromagnetic currents. This current generates a magnetic field and the object acts like a magnet. The electric current controls the magnetic field’s strength completely.

Characteristics of Magnets

• The magnets have attractive property that helps them prove their magnetic strength at the pole end.
• They also have a directive property that helps to understand the geographic direction in free air.
• The law of magnetic poles states “Like poles repel while unlike poles attract”.
• A magnet always has two poles that are north and the south pole. This is their pair property.
• The sure test of magnetization helps to discover if the rod is magnetized or not by checking its reaction to magnets.

Uses of Magnets

• They are common in magnetic needles and compass for mariners.
• The permanent agents are usually present in generators and electric motors.
• The electromagnetic ones are useful for speakers and electric bells.
• They are useful to separate iron filling from other solids.

Types of Magnetic Materials

There are three main kinds of magnetic behavior on which basis there is a division of magnetic materials. They are –

Diamagnetic Materials

They have very low magnetic properties even when under the magnetic fields. The magnetic dipoles usually get opposite to the applied field in these materials. This is because they have an internal magnetic field that repels the outer field.

And as soon as the outer magnetic field vanishes, the internal one disappears too. Some common examples are gold and mercury.

Paramagnetic Materials

In this case, the dipoles attract the outer magnetic field and align with it. In order to attract this material, the magnetic field must be very strong. But they are again not permanent magnets and lose the property as soon as they step out of the field.

Madame Curie is behind the discovery of this material. Her theory said that the external magnetic field and temperature impacts the magnetization. Some examples are – Liquid oxygen, salts of iron, and nickel.

Ferromagnetic Materials

They have the strongest magnetic behavior. The arrangement of magnetic dipoles is in such a way that they produce strong magnetic fields. The domains are present randomly and cancel each other’s fields and thus the entire material is not magnetic.

But in the presence of an external field, the internal reinforces and the whole object has strong magnetic fields.

After the removal of the external field, most domains continue to align with the field and this is common in permanent magnets. Some examples are – Iron, cobalt, nickel, neodymium, etc.

List of Magnetic Materials

Curie’s law

The curie law states that “ the magnetization in a paramagnetic material is directly proportional to the applied magnetic field”. Pierre Curie was a French physicist and the one behind this discovery. In the case of heating the object, the magnetic property is inversely proportional to the temperature.

The curie temperature turns the ferromagnetic material to paramagnetic with heat. This is commonly used in optical storage media for new data insertion. Though this law works better for higher temperatures than the magnetic fields. The equation of the law is –

M = C x (B/T)
(M – Magnetism, B – Magnetic field, T – absolute temperature and C = Curie constant)

Theory of Earth’s Magnetism

The Dynamo Effect is one theory to explain the earth’s magnetism. The outer core of the earth has metallic fluid. This fluid has magnetic fields because of the presence of iron. This is why the earth has its own magnetic fields.

The convection current in this layer generates magnetic properties. This is because they carry streams of charged particles. This field also ensures that the ionized charge coming from the sun does not enter the atmosphere.

This solar wind is capable of destroying the earth and this is why Mars does not have a strong atmosphere as there is no magnetic field. The earth’s magnetic poles are different from the geographic poles as Canada is the south pole while Antarctica is the north pole.

They are included by 10 degrees from the axis of the earth. The three components impact magnitude and direction of the earth’s magnetic field are –

Magnetic Declination
It is the angle between the real north and the magnetic north. On a flat plane, the true north keeps changing as the position of the earth keeps changing as it rotates.

Magnetic Inclination
This is the angle of dip as it is the angle of the earth’s surface at a horizontal plane. At the magnetic equator the dip becomes 0 degree while at the magnetic pole, it becomes 90 degrees.

Horizontal component of the earth’s magnetic field
There are two components that explain the intensity of the earth’s magnetic field. They are the Horizontal component (H) and the Vertical component (v).

Magnetic Flux

The total number of magnetic field lines passing through a closed surface is the magnetic flux. It provides a measurement of the magnetic field passing by. Greek letter Phi or Phi (B) denotes the magnetic flux or Φ or ΦB.

A flux meter usually measures this. The SI unit is Weber (Wb) and the fundamental unit is Volt/seconds.

The magnetic flux density is the force on per unit current in a wire placed at a right angle. Its SI unit is Tesla and the fundamental unit is Gauss. The formula for flux is

ϕB = B.A = BAcosΘ
(ΦB – magnetic flux, B – magnetic field, A – area, and θ t- angle at which the field lines pass)

Electromagnetic Induction

Micahel Faraday is an important name as he was behind the discovery of electromagnetic conduction. James Clerk Maxwell described it as Faraday’s law of induction.

The changing magnetic field produces voltage and thus current enabling electromagnetic induction. This is possible when the conductor is in the magnetic field whether in motion or stationary.

The experiment by Faraday recognized two factors affecting voltage production. They were the number of coils and their direct proportion to voltage. The more turns, the more voltage.

The second factor was changing magnetic fields and their movement around the conductor. The experiment used magnets and electric circuits to study the factors.

Applications of Electromagnetic Induction

1. The AC generator follows this principle
2. The working of electrical transformers
3. The magnetic flow meter
4. Electric motors

Electromagnetic Induction Formula

e = N × dΦ / dt
(e – induced voltage, N – number of turns in the coil, Φ – magnetic flux, and t – time)

Mutual Induction

It is the coiling property to oppose the changes in the current of another coil. The change in one coil’s current changes the flow and eventually induces EMF in other coils as well. This process is mutual induction.

A transformer follows this concept as it has a primary coil for input and a secondary one for output. The microphone also follows the same idea.

An insulator usually makes the core part which connects the coil. It also has a shunt that absorbs reactivity and improves efficiency.

The readings of the diagram are –

• Np – No. of turns in the primary winding
• Ns – No. of turns in the secondary winding
• Ip – Current flowing in the primary
• Is – Current flowing in the secondary
• Vp – Voltage across the primary
• Vs – Voltage across the secondary
• Φ – Magnetic flux present around the core

Alternative Current

An electrical generator is capable of converting mechanical energy to electrical energy and is often known as a dynamo. This model has a rectangular coil present in a uniform magnetic field coming from a permanent magnet.

In this case, alternating current is the electric current that changes frequency and flows opposite to direct current. This change takes place at regular time intervals.

The particles in AC begin at zero and keep on increasing and falling creating a cycle. This cycle keeps on repeating at a regular time interval. They usually have alternating voltages and are capable of transforming from a higher to lower voltage level. The device with this current is alternators.

The other method to generate it is by using a single coil generator transformed from a higher voltage level to a lower voltage level. An alternating current can transmit power at a larger distance with less energy.

Application of Alternating Current

• Home appliances
• Audio signal
• Radio signal

Ammeter

It is responsible for measuring the magnitude of the current flowing in a circuit. The magnetic field is not mandatory for its functioning. Ammeter is capable of measuring alternate and direct current and is more accurate.

It can work as both a mechanical or electronic device. It is present in an electric circuit and is less sensitive.

Galvanometer

It is responsible for measuring the strength and direction of small currents. Galvanometer needs a mandatory magnetic field to function properly and measure only direct current. It is present only as a mechanical device and is less accurate. It is sensitive and is usually used as a potentiometer.

Voltmeter

It is responsible for measuring the voltage across two points and requires a magnetic field to function. Voltmeter has very high resistance and can change the range.

It shares a parallel connection with circuit series and has lower accuracy. The ideal resistance is infinity for it to function. V denotes this measurement device.

Conclusion

The magnets are present in our daily lives in many applications. This makes the concept of magnetism very important for general science modules. This topic is very relevant for exams like UPSC, RRB, SSC, etc. Some important topics were the magnetic fields, earth’s magnetism, currents, and much more.

The General Science paper of the UPSC exam might have a question from this. The Prelims have a higher chance of getting this under general science paper.

This is because it comes under the physics basic level module and is present in NCERT books as well. Candidates should consider reading this article to improve their basic science for exams.