Magnetism JSS3 Basic Science Lesson Note

Loadstone is a naturally occurring magnetic oxide of iron or natural magnet. It was discovered in China 2000 years ago. Loadstone is a magnetic mineral that attracts iron and steel objects. When loadstone is suspended it swings freely and it always points to the direction of north and south.

Laws of magnet

–like poles repel each other

-unlike poles attract each other.

Magnetic poles and field

A  suspended magnet will swing and finally rest in the direction of north-south. The end of a magnet pointing towards the geographical north pole is the south pole of the magnet while the end of the magnet pointing to the geographical pole is the north pole of the magnet.

Magnetic field /magnetic domain is defined as the space or regions surrounding the magnet where magnetic force can be felt.

-The uniform earth field and the lines of forces are parallel and equally spaced

-Field for two isolated poles e.g. N-S lines run from the north to the south pole

-Two isolated similar poles N-N with a neutral point occurring in-between.

The ends of the poles are called the poles.

The strongest force on a magnet is found at the ends of the magnets.

Diagram

Care or Maintenance of magnet

1. By using a keeper is a piece of iron that is temporarily added between the north and south poles of a magnet to prevent demagnetization by redirecting the magnetic field.
2. Magnets should be stored in pairs.
3. Store in a dry place.
4. Store in a non –ferromagnetic container
5. Store in a cool place
6. Magnets may be coated or capped to prevent corrosion.
7. Magnet should not be heated as this will destroy the magnetic properties

 USES OF MAGNETS

Magnets are useful in the following areas such as

-radio communication

–telegraph

-in appliances such as computers, electric generators, loudspeakers, microphones and  electromagnets

ASSIGNMENTS

1.  Magnet is made from   A. iron  B.tin  C.copper  D.steel
2. Loadstone is a naturally occurring magnet discovered in  A.Britain  B.America  C.Germany China
3. Which of the following statements is correct?  A.unlike poles repel  B. like poles attract  C.like poles repel  D.unlike poles repel and attract
4. The following exert a field force except?   A.magnet and pin  B.electric force   C.dragged table  D. comb and hair.
5. A bar magnet has ________ poles   A. one   B.two three D.four
6. Magnet is used in all of the following except in  A. cookers   B.telegraph  C generator  D. loudspeakers.

7a.Explain  how to show magnetic force  around a magnet

b.Demonstrate how to detect the North And South poles of a magnet