Magnetic Field Lines – Class 12 | Chapter – 5 | Physics Short Notes Series PDF for NEET & JEE

Magnetic Field Lines: Magnetic field lines are a way to visualize the direction and strength of a magnetic field. They are imaginary lines that are drawn to represent the direction of the force that a small magnet or magnetic material would experience if placed in the field.

Characteristics of Magnetic Field Lines

Some key characteristics of magnetic field lines include:

  • They always form closed loops, never beginning or ending in space.
  • They are continuous, with no gaps or breaks in the lines.
  • The direction of the field lines indicates the direction of the magnetic force that a small magnet or magnetic material would experience if placed in the field.
  • The density of the field lines represents the strength of the magnetic field, with more closely spaced lines indicating a stronger field.
  • The field lines never intersect or cross each other.
  • The direction of the field lines is always from the north pole of a magnet to the south pole outside the magnet, and from the south pole to the north pole inside the magnet.

Types of Magnetic Field Lines

There are two main types of magnetic field lines:

  • Closed magnetic field lines: These field lines form closed loops and never intersect. They are found around permanent magnets and are also present in the magnetic fields of some planets, such as Earth.
  • Open magnetic field lines: These field lines extend outward from a magnetic object and do not form closed loops. They are found in the magnetic fields of stars, including the Sun, and are also present in some laboratory plasmas.

In addition, magnetic field lines can be further classified based on their shape and behavior, including:

  • Straight magnetic field lines: These field lines are straight and extend outward from a magnetic object, with their density decreasing as they move away from the object.
  • Curved magnetic field lines: These field lines curve around a magnetic object, following the shape of the object’s magnetic field.
  • Focused magnetic field lines: These field lines converge at a point, creating a strong magnetic field in a small region.
  • Divergent magnetic field lines: These field lines spread out from a point, creating a weaker magnetic field over a larger area.

Properties of Magnetic Field Lines

Some important properties of magnetic field lines include:

  • They form continuous loops: Magnetic field lines always form continuous loops, never beginning or ending in space.
  • They have direction: The direction of the magnetic field lines indicates the direction of the magnetic force that a small magnet or magnetic material would experience if placed in the field.
  • They never intersect: Magnetic field lines never intersect or cross each other, which means that the magnetic force at any point is always in a single direction.
  • They are more dense where the field is stronger: The spacing of the magnetic field lines represents the strength of the magnetic field, with more closely spaced lines indicating a stronger field.
  • They always form closed loops around a magnetic object: Magnetic field lines always form closed loops around a magnetic object, with the direction of the field lines being from the north pole to the south pole outside the magnet, and from the south pole to the north pole inside the magnet.
  • They can be used to visualize magnetic phenomena: Magnetic field lines provide a useful tool for understanding and visualizing magnetic phenomena, such as the behavior of magnets, the interaction between electric currents and magnetic fields, and the structure of planetary and stellar magnetic fields.

Magnetic Field Lines around a Bar Magnet

The magnetic field lines around a bar magnet form a pattern that resembles a series of loops that extend from the magnet’s north pole to its south pole. Some key features of these magnetic field lines include:

  • The magnetic field lines are continuous and form closed loops.
  • The magnetic field lines are strongest near the poles of the magnet, where they are tightly packed together.
  • The magnetic field lines curve away from the magnet’s north pole and towards its south pole.
  • The magnetic field lines never intersect or cross each other.
  • The direction of the magnetic field lines indicate the direction of the magnetic force that a small magnet or magnetic material would experience if placed in the field.
  • The spacing of the magnetic field lines indicates the strength of the magnetic field, with the lines being more closely spaced where the field is stronger.
  • The magnetic field lines extend both inside and outside of the magnet, with the direction of the field reversing between the two poles of the magnet.


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By Team Learning Mantras