Magnetic phenomena are found worldwide. Magnetic fields from several sources permeate throughout the universe, penetrating stars, planets, atoms, humans, and maybe extraterrestrial beings. Magnetism is prevalent on Earth even before the birth of humanity. The Earth’s magnetic field has been present from when Earth was formed. This article will focus on magnetism, its properties, certain laws of physics about magnetism, etc. All the topics covered in this article are from the CBSE class 12 board examination point of view. You can visit the CBSE Class 12th datasheet which has been released.
History of Magnets
The word magnet comes from the Greek island of Magnesia, where magnetic metal reserves were discovered in the early 600 BC. Shepherds were stuck between the rocks when their iron-tipped rods were placed on the ground. Their shoes (the sole made of iron nails) suffered the same fate. The magnetic properties of the rocks made it tough for them to walk around.
Curiosity Enough: The Chinese are largely credited for the technological application of magnets. Magnetic needles are mentioned in Chinese writings dating back to 400 BC. Magnetic needles were also used by caravans crossing the Gobi desert.
Some Features of Magnets
The following are well-known magnetism concepts:
The earth acts like a magnet, with its magnetic field extending roughly between geographical south and north.
The magnet’s north pole is the tip that refers to the geographic north, while the south pole is the tip that refers to the geographic south.
When two north poles or two south poles are placed near together, they repel each other. But the closed-loop pole of one magnet is placed next to the south pole of another magnet. They experience an attractive force.
A magnet’s north and south poles cannot be separated. When a bar magnet is split in half, two smaller bar magnets with weaker magnets are formed, with a north and a south pole. A magnet can never exist with one pole; hence magnetic monopoles are impossible.
Magnets can be made from iron and other ferromagnetic alloys.
Bar Magnet: Definition and Properties
A bar magnet is one of the simplest magnets, which is a rectangular bar that points towards geographical North and South when suspended in free space.
The Magnetic Field Lines
Do this at home. Take a bar magnet and place it under a thick sheet of paper. Sprinkle some iron filling on the paper and notice how a specific pattern draws on the paper. You will get a pattern similar to the image displayed below:
You can draw the pattern of the magnetic field line using this pattern formed by iron fillings. You can say that magnetic field lines visualize how a magnetic field exists in a magnet. Listed below are some very important properties of magnetic field lines. Read them very carefully:
- The magnetic field lines are in the shape of a closed-loop. They travel from the north pole to the south pole outside the magnet and come back from the south pole to the north pole inside the magnet, forming an endless loop.
- The net magnetic field B path at a particular position is represented by drawing a tangent to the field line at that point. The direction of the tangent is the direction of the magnetic field.
- Per unit area, the magnitude of the magnetic field B is directly proportional to the number of lines crossing through that area.
- No two magnetic field lines intersect each other. If they crossed each other, we would have two directions for the same magnetic field, which is impossible.
The area within which a magnetic substance begins to attract towards the magnet is known as the magnetic field. The value of the magnetic field caused by a bar magnet can be formulated using the formulas given below:
For large distances K >>> k (Here K is the distance of the bar magnet and k is the length of the bar magnet)
The equatorial field: B → – m 4 (K)3
The axial field: B → 2m 4 (K)3
‘m’ is the magnetic moment.
The Dipole in a Uniform Magnetic Field
It may be necessary to precisely identify the amount of Bx many times during our calculations. This is accomplished by placing a small compass needle with the moment of inertia ‘I’ and constant magnetic moment closed-loop shaped and allowing it to oscillate. The torque present on the needle is formulated as:
τ = m × Bx (this is a vector quantity so, please follow vector multiplication)
In magnitude τ = mBx sin
Here τ is known as the restoring torque and is the angle between m and Bx.
To study this concept in detail, kindly visit the JEE Main physics syllabus page.
Also Read: Electromagnetic Induction | Units Of Magnetic Fields
Gauss’s Law of Magnetism
In any closed surface, the number of magnetic field lines passing through it is governed by Gauss’ Law. The area vector here is pointing away from the surface. The gauss surfaces the magnetic field lines which go out from the surface retracts their path and comes back because magnetic field lines are continuous loops. As a result, a closed surface’s net magnetic flux is zero.
The total flux ϕ = ∫B.dA = 0.
Earth’s Magnetism
We all know that Earth has a magnetic field, but scientists to date don’t know how it was created or what keeps it running. From the CBSE Board exam point of view, you are asked how to find the value of Earth’s magnetic field at any given point. Listed below are the three parameters that are essential for the measurement, they are:
Magnetic Declination: Magnetic declination is the angle formed by the magnetic meridian and the geographic meridian at a specific place.
Magnetic Dip or Magnetic Inclination: Magnetic dip or magnetic inclination is the angle created by the direction of the entire magnitude of the Earth’s magnetic field and a straight horizontal line present in the magnetic meridian.
Horizontal Component: ‘H’ is used to represent the horizontal component. The magnetic meridian is the ‘cos’ component of the magnitude of the Earth’s magnetic field.
Classification of Magnetic Materials
The Earth consists of tons of different elements and their compounds by combining. Thus it wasn’t easy to classify the magnetic materials from the normal ones until Faraday researched them and grouped them based on their magnetic properties. He divided the materials into:
Diamagnetic Substances
Individual atoms in diamagnetic materials do not have a net magnetic moment. When subjected to an external magnetizing field, such substances get slightly magnetised in the reverse direction of the magnetic field. When exposed to a non-uniform magnetic field, these substances tend to move from stronger portions of the magnetic field to meeker areas. Magnetic field lines never move inside a diamagnetic material specimen when placed in a magnetizing field. Diamagnetic materials have a relative magnetic permeability of less than one at all times. This results in the susceptibility of diamagnetic materials to a smaller negative value.
Paramagnetic Substances
Each atom of a paramagnetic substance has a magnetic moment amounting to something more than zero. When subjected to an external magnetic field, such materials become weakly magnetized in the field’s direction. When kept in a non-uniform magnetic field, they migrate from less strong to stronger regions of the field.
Instead of moving in free space, the magnetic field lines move from inside when a paramagnetic material specimen is placed in a magnetizing field. As a result, paramagnetic materials’ susceptibility is positive, albeit slight. The susceptibility varies inversely with their temperature; as the temperature rises, they lose their magnetic property.
Ferromagnetic Substances
Ferromagnetic materials, unlike paramagnetic materials, have a non-zero magnetic moment. Ferromagnetic materials have all of the features of paramagnetic materials but to a much greater level. Each atom gets extremely magnetized in the direction from which the magnetic field is applied. For example, Iron is the best-known ferromagnetic substance. As you increase the temperature of any ferromagnetic substance, it loses its magnetic properties. It turns to a paramagnetic substance and, on further heating, changes to a diamagnetic sense.
Also See: Electromagnetic induction concept for class 12 physics
Curiosity Enough: The ferromagnetic material turns to a paramagnetic material at a certain temperature. This is known as Curie temperature. Named after the famous scientist Pierre Curie, who discovered this phenomenon. Iron, for example, has a Curie temperature of roughly 1000 K.
Permanent Magnets
Permanent magnets are materials that retain their ferromagnetic properties at room temperature for an extended period.
To make a robust permanent magnetic a substance must have the following three properties:
- High Retentivity: To make the magnet strong.
- High Coercivity: To make the magnet durable for temperature changes, improper handling, and the influence of different magnetic fields.
- High Permeability: To make the material well suited for magnetization.
Steel is the best material for making affordable and durable permanent magnets.
We all know that if electricity passes through a conducting material, it forms an electric and magnetic field. Using this concept, electromagnets are made. The material used for electromagnets should be ferromagnetic at the core, with strong permeability and weak retentivity. Soft Iron is the best choice for making electromagnets.
The magnetic field of a solenoid is amplified by a thousand when a soft iron rod is placed into it, and a current is passed through it. Because soft Iron has a low retentivity, the magnetism is instantly removed when the current in the solenoid is switched off. Electromagnets are used in electric bells and at the junkyard, cranes lift machines, and other stuff using powerful electromagnets.