Simple phenomena of magnetism

MAGNETS:#

• Magnets have a magnetic field around them

• They 2 opposite poles (North and South) which exert forces on other magnets. Like poles repel and unlike poles attract. This is caused by the interaction of magnetic fields.

  • Therefore, if magnets are facing each other with opposite poles, they will come together given a small space between them

• They attract magnetic materials by inducing (permanent or temporary) magnetism in them.

• Will exert little or no force on a non-magnetic material

• The direction of an electric field at a point is the direction of the force on a positive charge at that point

• Induced Magnetism:

  • Magnets attract materials by inducing magnetism in them; the material becomes a magnet as well.

  • The side of the material facing the magnet will become the opposite pole as the magnet.

• Methods of inducing magnetism:

• A piece of steel becomes permanently magnetized when placed near a magnet, but its magnetism is usually weak.

• It can be magnetized more strongly by stroking it with one end of a magnet

• Most effective method: place it in a solenoid and pass a large, direct current (d.c.) through the coil.

• Methods of demagnetisation:

  • If a magnet is hammered, its atomic magnets are thrown out of line and it becomes demagnetized.

  • Heating a magnet to a high temperature also demagnetize it.

  • Stroking with another magnet to destroy the alignment of poles

  • Place magnet with poles opposite to that which is induced by a d.c. current and insert into coil with d.c. current

  • Most efficient method: place magnet inside a solenoid connected to an alternating current (a.c.) supply.

• Soft Iron vs. Steel

Permanent Magnet vs. Electromagnet