Key Concepts in Magnetism

Key Concepts in Magnetism

Magnetism is the property displayed by magnets and produced by the movement of electric charges, which results in objects being attracted or pushed away.

Magnet

A magnet is a piece of iron or other material that can attract iron-containing objects and points north and south when suspended.

Properties of a Magnet

1. Attractive Property:

• A magnet attracts magnetic substances like iron, cobalt, nickel, and some of their alloys like magnetite.

2. Directive Property:

• When a magnet is freely suspended, it aligns itself in the geographical north-south direction.

Types of Magnets

1. Natural Magnets:

• A natural magnet is the oxide of iron, but due to its irregular shape, weak magnetism, and high brittleness, natural magnets are not used in laboratories.

2. Artificial Magnets:

• Magnets made by artificial methods are called artificial magnets or man-made magnets.

• Types of artificial magnets include bar magnets, magnets, Robinson's ball-ended magnets, magnetic needles, electromagnets, etc.

Magnetic Poles

The two points near the ends of a magnet where the attracting capacity is maximum are called magnetic poles.

• When a magnet is freely suspended, one pole always directs towards the north. This pole is called the North Pole.

• The other pole is called the South Pole.

Magnetic Axis

• The imaginary line joining the two poles of a magnet is called the magnetic axis of the magnet.

Magnetic Behavior

• Similar poles repel each other.

• Dissimilar poles attract each other.

• The middle part of a magnet has the minimum magnetic power.

Magnetization by Induction

• When a magnetic substance is placed near a magnet, it gets magnetized due to induction.

Magnetic Field

• The region in space around a magnet where the magnet has its magnetic effect is called the magnetic field of the magnet.

Magnetic Flux Density

• Magnetic flux density of a point in a magnetic field is the force experienced by a north pole of unit strength placed at that point.

• The SI unit of magnetic flux density is newton/ampere-meter or weber/meter² or tesla (T).

Magnetic Lines of Force

The magnetic lines of force are imaginary curves representing a magnetic field graphically. The tangent drawn at any point on the magnetic lines of force gives the direction of the magnetic field at that point.

Properties of Magnetic Lines of Force

1. Magnetic lines of force are closed curves. Outside the magnet, they travel from the north to the south pole, and inside the magnet, they travel from the south to the north pole.

2. Two lines of force near each other never intersect.

3. If the lines of force are crowded, the field is strong.

4. If the lines of force are parallel and equidistant, the field is uniform.

Magnetic Substances

Based on magnetic behavior, substances can be classified into three categories:

Diamagnetic Substances:

• These substances acquire feeble magnetism opposite to the direction of the magnetic field.

Examples: Bismuth, Zinc, Copper, Silver, Gold, Diamond, Mercury, Water, etc.

Paramagnetic Substances:

• These substances acquire feeble magnetism in the direction of the magnetic field.

Examples: Aluminum, Platinum, Manganese, Sodium, Oxygen, etc.

Ferromagnetic Substances:

• These substances are strongly magnetized in the direction of the magnetic field.

Examples: Iron, Cobalt, Nickel, etc.

Magnetic Domains

• Atoms of ferromagnetic substances have a permanent dipole moment, meaning they behave like very small magnets.

• The atoms form large regions called domains, in which millions of atoms have their dipole moment aligned in the same direction.

Curie Temperature

• As the temperature increases, the magnetic property of ferromagnetic substances decreases.

• Above a certain temperature, these substances transform into paramagnetic substances.

• This temperature is called the Curie temperature.

Types of Magnets

• Permanent Magnets: Made of materials like steel, cobalt steel, ticonal, alcomax, and alnico.

• Electromagnets: Cores made of soft iron, mu-metal, and stalloy are used in transformers, telephone diaphragms, dynamos, and motors.

Terrestrial Magnetism

The Earth behaves like a powerful magnet with its south pole near the geographical North Pole and its north pole near the geographical South Pole. The magnetic field of the Earth at a place is described in terms of the following three elements:

1. Declination:

• The acute angle between the magnetic meridian and the geographical meridian at a place is called the angle of declination at that place.

2. Dip or Inclination:

• Dip is the angle that the resultant Earth’s magnetic field at a place makes with the horizontal. At the poles and equator, dip is 90° and 0°, respectively.

3. Horizontal Component of Earth's Magnetic Field:

• It is defined as the component of Earth’s magnetic field along the horizontal in the magnetic meridian. Its value differs at different places (approximately 0.4 gauss or tesla).

Magnetic Maps

Magnetic maps are geographical maps that show the values of the three magnetic elements of the Earth.

Important Lines on Magnetic Maps

1. Isogonic Lines: Lines joining places with the same declination.

2. Agonic Line: The line joining places with zero declination.

3. Isoclinic Lines: Lines joining places with the same dip.

4. Aclinic Line: The line joining places with zero dip (also called the magnetic equator).

5. Isodynamic Lines: Lines joining places with the same value of the horizontal component of the Earth’s magnetic field.

Final Thoughts

Magnetism is a fundamental property of matter, exhibited by magnets, which are materials that produce magnetic fields due to the movement of electric charges. Magnets have two key properties: attractive (they attract materials like iron, cobalt, and nickel) and directive (they align themselves in the north-south direction when suspended).

There are two types of magnets: natural (found in nature) and artificial (man-made, such as bar magnets and electromagnets). The magnetic poles at each end of a magnet have the strongest attracting force.

Magnetic fields are represented by magnetic lines of force, which are closed curves showing the direction of the magnetic field. Magnetic substances are classified into diamagnetic, paramagnetic, and ferromagnetic categories based on how they react to magnetic fields.