Magnetic Field and Related Terms

Moving charges or electric current generates a magnetic field.

Hans Christian Oersted (1777-1851)

Oersted showed that electricity and magnetism are related to each other. His research later used in radio, television etc.

The unit of magnetic field strength is named Oersted in his honor.

Oersted Experiment

Oersted Experiment

On passing the current through the copper wire XY in the circuit, the compass needle which

Is placed near the conductor gets deflected. If we reverse the direction of current, the compass needle deflects in reverse direction. If we stop the flow of current, the needle comes at rest.

Hence, it can be concluded that electricity and magnetism are linked to each other.

It shows that whenever the current will flow through the conductor, then a magnetic field will develop.

General Terms Related to Magnetic Field

Magnetic Field

It is the region surrounding a magnet, in which force of magnet can be detected. It is a vector quantity, having both direction & magnitude.

Compass Needle

It is a small bar magnet, whose north end is pointing towards north pole and south end is pointing towards south pole of earth.

Magnetic Field Lines

The tangent to the magnetic field line at a point gives the direction of magnetic field at that point.

Magnetic Field Lines

Hence, magnetic field line is a path along which a hypothetical free north pole tends to move towards south pole.

Properties of Magnetic Field

  • The magnitude of magnetic field increases with increase in electric current and decreases with decrease in electric current.
  • The magnitude of magnetic field produced by electric current decreases with increase in distance and vice-versa.
  • The size of concentric circles of magnetic field lines increases with distance from the conductor, which shows that magnetic field decreases with distance.
  • Magnetic field lines are always parallel to each other.
  • No two field lines cross each other.

Characteristics of Magnetic field lines

  • The direction of magnetic field lines outside the magnet is always from north pole to south pole of bar magnet and are indicated by an arrow. Inside the magnet, the direction of field lines is from its south pole to north pole. Thus, magnetic field lines are closed curves.
  • The strength of magnetic field is expressed by the closeness of magnetic field lines. Closer the lines, more will be the strength and farther the lines, less will be the magnetic field strength.
  • No two field lines will intersect each other. If they intersect, then at point of intersection the compass needle will show two directions of magnetic field which is not possible.



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