FORM TWO TOPIC THREE -MAGNETISM

3.0    MAGNETISM

3.1 Concept of magnetism

Ø  The magnetism –comes from a region called magnesia

Magnesia – meaning ‘a mineral’

A magnet is any material that has properties similar to those of the iron ore.

A bar magnet

Magnetic and non-magnetic materials

Magnetism –is the force that is in existence almost everywhere

                     Or is the phenomenon of physical attraction for iron that is common in magnets.

Induced magnetism –is the resultant force introduced to materials (steel or iron) becomes a magnet due to its nearness or contact with a magnet.

   Or is the resultant force that is transferred to steel or iron by being near or within magnetic field of a magnet.

Ø  It could be permanent or temporary magnetism

Induction –is the process by which a material becomes a magnet due to its nearness or contact with a magnet.

Ferromagnetic materials –is the materials that can magnetised strongly.

Properties of magnets

        i.            Magnets attract magnetic materials

      ii.            The magnetic force is an action at a distance force

    iii.            The magnetic force is strongest near the poles of a magnet

     iv.            Like poles repel each other while unlike poles attract

       v.            The north pole of a freely moving magnet points south and the south points north of the earth’s magnet.

Types of magnets

        i.            Temporary magnets

      ii.            Permanent magnets

    iii.            Electromagnets

Application of magnets

        i.            Magnetic recording media

      ii.            Credit, debit and ATM cards

    iii.            Speakers and microphones

     iv.            Electric generators

       v.            Transformers

     vi.            Common television and computer monitors

   vii.            In hospitals when dealing with eye injuries caused by iron or steel splinters.

    3.2 Magnetization and demagnetization

Magnetization –is the process of aligning the domains of atoms in a material in one direction so as to produce a net effect of attraction or repulsion. It is the process of making magnets

Magnetic domains –is the magnetic dipoles arrange themselves in groups

Magnetic dipoles –is the atoms of magnetic materials that behaves like tiny magnets.

Ferromagnetic materials –is the materials that can be magnetised strongly.

Paramagnetic materials –is the materials that can be temporary magnetised

Ø  The alignment of domains in the materials.

        i.            By heating or vibration

      ii.            Stroking method

    iii.            Electric method (solenoid)

     iv.             

Demagnetization

Demagnetization –is the opposite process of magnetization

                              Or is the process of removing magnetization.

Ø  The process of undo the alignment of domains to materials

        i.            The permanent magnet is heated or vibrated in absence of external field

      ii.            Randomly stroking one magnet with another

    iii.            Wrapping a wire coil around the magnet and coil connecting with alternating current.

     iv.            Repeat hammering or dropping down of the magnet.

Storage of magnets

Ø  To maintain the magnetism in magnets for a long period of time.

        i.            Avoid storing magnets in places where in contact with ferrous object such as steel shelves and tools

      ii.            Store magnet in pairs with unlike pole facing each other

    iii.            Do not overheat a magnet.

     iv.            Do not store magnet near strong magnetic or electric fields

    3.3 Magnetic fields of a magnet

Magnetic field –is the area or region around a magnet

                         Or is the region around a magnet in which magnetic materials are attracted by the magnet

Ø  Magnetic line is represented by the lines of action of magnetic force called field lines.

Magnetic lines of force

Magnetic lines of force –is the line that run from the North Pole to the south pole of a magnet.

Ø  The properties of magnetic lines of force

                    i.            Magnetic lines of force are continuous and will always form closed loops.

                  ii.            Lines of force start at the north pole and end at the south pole

                iii.            Magnetic force is stronger where the lines are close together and weaker where they are far apart

                 iv.            Magnetic lines of force will never cross one another

                   v.            Parallel magnetic lines of force travel in the same direction repel one another

Neutral points in a magnetic field

Neutral points –is the points where the net magnetic field is zero

Ø  Has no magnetic field

Magnetic shielding

Magnetic shielding –is the process of limiting the flow of magnetic fields between two locations by separating them with a barrier made of conductive materials.

       3.4 Earth’s magnetic field

Direction of the earth’s magnetic field

A compass –is a device with a magnetised needle that is free to rotate in a horizontal plane and align itself with the horizontal component of the earth’s magnetic field.

The magnetic meridian –is a vertical plane in which the magnet comes to rest with its axis.

Earth’s magnetic lines of force about a bar magnet

Angle of declination

Angle of declination –is the angle between the geographic north and the magnetic north

Angle of inclination (dip angle)

Angle of inclination (dip angle) -is the angle between the magnetic field and the earth’s surface.

Applications of the earth’s magnetic field

        i.            It is used by map-readers for finding locations of different places.

      ii.            It gives useful information in the search for materials.

    iii.            Satellites fitted with magnetometers can transmit information about the earth’s magnetic field high above the surface.

     iv.            Map-readers with a magnetic compass can locate the direction of the magnetic north using the compass.