Magnetism
Magnetism is a special trait that magnets have, and it happens when electric charges move around. It makes things either stick together or push each other away. A magnet is something made of iron or other materials that can pull objects made of iron towards it and always points north and south when you hang it up.
Magnets have two main qualities: they attract things made of iron, like nails, and they always point in a certain direction when you let them hang freely, like on a string.
There are two types of magnets: natural ones, which are made of iron oxide but aren't very strong or useful, and artificial ones, which we make ourselves. Artificial magnets come in different shapes and types, like bar magnets or horseshoe magnets.
The ends of a magnet are called poles, and they're where the magnet's pulling power is strongest. One pole always points north when the magnet is hanging freely. That's called the north pole, and the other end is the south pole.
The line that connects the two poles of a magnet is called its magnetic axis. When you put two magnets together, the same poles push each other away, and opposite poles pull together.
When you bring a piece of iron close to a magnet, it can become a magnet itself for a while. That's called induction.
Magnetic Field: The area around a magnet where its magnetic power can be felt is called its magnetic field.
Intensity of Magnetic Field or Magnetic flux density: It's the strength of the magnetic field at a specific point. It's measured by the force a north pole of unit strength would feel at that point. Its unit can be written as N/A·m, Wb/m², or T.
Magnetic Lines of Force: These are imaginary lines that show the direction a magnetic field takes around a magnet. Drawing a tangent at any point on these lines tells us the direction of the magnetic field at that spot.
Properties of Magnetic Lines of Force:
- They form closed loops. Outside the magnet, they go from north to south, and inside, they go from south to north.
- They don't intersect each other.
- When they're close together, the magnetic field is stronger.
- If they're evenly spaced and parallel, the magnetic field is uniform.
Magnetic Substances: There are three types based on how they behave in a magnetic field.
Diamagnetic Substances: These substances, like bismuth or water, weakly oppose the magnetic field's direction.
Paramagnetic Substances: Materials such as aluminum or oxygen weakly align with the magnetic field's direction when placed within it.
Ferromagnetic Substances: Substances like iron or nickel become strongly magnetized in the direction of the magnetic field when placed within it.
Curie Temperature: When the temperature rises, the magnetic properties of a ferromagnetic substance weaken. Beyond a certain temperature, called the Curie temperature, the substance transforms into a paramagnetic substance.
Materials used for Permanent Magnets: Steel, cobalt steel, ticonal, alcomax, and alnico.
Materials used for Electromagnets and Transformer Cores: Soft iron, mu-metal, and stalloy.
Terrestrial Magnetism :
Our planet acts like a giant magnet, with its south pole close to the geographic north pole and its north pole near the geographic south pole. When we talk about the magnetic field at the Earth's poles, we use three main terms:
Declination (D): It's the angle between the direction of the magnetic field and the direction of true north. Positive declination means magnetic north is east of true north, and negative declination means it's west.
Dip or Inclination (I): It's the angle at which the magnetic field lines dip below the horizontal. At the poles, it's 90° (straight down), and at the equator, it's 0° (parallel to the surface).
Horizontal Component (H): It's the strength of the magnetic field in the horizontal direction. It varies from place to place but is around 0.4 gauss or 0.4 x 10−4 tesla globally.
Magnetic Maps: These are maps that show the values of three magnetic elements of the Earth.
Important Lines on Magnetic Maps:
Isogonic Lines: These are lines that connect places with the same declination, or the angle between magnetic north and true north.
Agonic Line: This line connects places where there is zero declination, meaning magnetic north aligns perfectly with true north.
Isoclinic Lines: These lines connect places with the same dip, or the angle at which magnetic field lines tilt from the horizontal.
Aclinic Line: This line connects places where there is zero dip, also known as the magnetic equator.
Isodynamic Lines: These lines connect places with the same value of the horizontal component of the Earth's magnetic field.
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