Magnetism

• First known magnetic pieces were of lodestone which is an ore of Iron oxide found in Magnesia in Asia Minor.
• If a magnet is suspended using a silk thread such that it is free to rotate in a horizontal plane, it always sets itself in the geographic north and south direction.
• The temporary magnetism acquired by a magnetic material kept near or in contact with a magnet is called induced magnetism. This process is known as magnetic induction.
• A magnetic pole induces an opposite polarity on the near end and a similar polarity on the farther end of the magnetic material.
• The space around a magnet in which the needle of a compass rests in a direction other than the geographic north and south direction is called magnetic field of the magnet.
• The distance of a point from the magnet increases, the effect of its magnetic field decreases.
• Magnetic field is a vector quantity.
• The magnetic field line is a continuous curve in a magnetic field such that tangent at any point of the curve gives the direction of the magnetic field at that point.
• Properties of magnetic field lines:

  • Closed and continuous curves
  • Directed from the north pole towards the south pole outside the magnet.
  • Never intersect one another.
  • Parallel and equidistant lines represent a uniform magnetic field.
  • Behave like stretched elastic rubber strings.
• Evidences of Earth's magnetic field:

  • A freely suspended magnetic needle always lies in the geographic north and south direction.
  • An iron rod buried inside the earth along the north and south direction becomes a magnet.
• Two places where a magnetic needle becomes vertical are called magnetic poles.

  The line joining the places where the magnetic needle becomes horizontal is called magnetic equator.
• Neutral points are points at which two magnetic fields are equal in magnitude but opposite in direction and the net magnetic field at these points is zero. A compass needle if placed at these points, will rest in any direction.