MAGNETISM ENOTE

WEEK ONE

SUBJECT: BASIC SCIENCE

TERM: SECOND

CLASS: GRADE 9

TOPIC: MAGNETISM

MEANING OF MAGNETISM: The force with which a magnet attracts magnetic substances and repels another magnet is called magnetism. A magnet is a substance which attracts objects made of iron. Magnet strongly attracts ferromagnetic materials such as iron, nickel, steel and cobalt. Magnet are found in ATM card, pin holders in which common pins remain stuck to the holder, stickers which remain attached to iron surfaces such as door of almirahs.

LOADSTONE (MAGNETITE, FE₃O₄) AS THE NATURALLY OCCURRING FORM OF MAGNETS: Loadstone also called lodestone is a naturally magnetized piece of the mineral magnetite. It is a naturally occurring magnet that attracts pieces of iron. Ancient people first discovered the property of magnetism in loadstone. Pieces of loadstone were suspended so that they could turn, and these were the first magnetic compasses. Their importance to early navigation is indicated by the name lodestone, which in middle English means ‘course stone’ or ‘leading stone’. Loadstone is one of only two minerals that is found naturally magnetized; the other pyrrhotite, is weakly magnetic. Magnetite is black or brownish-black with a metallic luster. Only a small amount of magnetite on the Earth is found magnetized as Loadstone.

LAWS OF MAGNETISM: Like pools of a magnet repel each other while unlike poles attract each other.

When a bar magnet is brought close to iron filings, More iron filings cling at the ends of the magnet whereas very less or no filings cling at the centre of the magnet. This shows that the strength of a magnet is maximal at its ends. These ends are called poles of a magnet.

   A freely floating or suspended magnet always points in a north-south direction. The end of the freely suspended magnet which points toward the geographic north is called North Pole of the magnet. Similarly, the end of a free suspended magnet, which points towards the geographic South is called South Pole of a magnet.

  When the north pole of one magnet is brought near the north pole of another magnet, they repel each other. Similarly, when the south pole of one magnet is brought near the north pole of another magnet, they attract each other. This shows that like poles of two magnets repel each other and unlike poles attract each other.

MAGNETIC POLES AND FIELDS: Magnets have two poles, called the North (N) and South (S) pole.

   The region around a magnet where its magnetic influence is felt consists of imaginary lines called magnetic lines of force. When a magnet is broken into pieces, then each piece behaves like a complete magnet. Thus, we can say that magnetic poles always occur in pair.

   You will observe that in a small space around the magnet, the iron fillings set themselves in the form of curves. The iron filings move and reposition themselves under the effect of magnetic field of the bar magnet. The paths along which iron filings adjust themselves in the magnetic field are the magnetic lines of force.

CARE OF MAGNETS: You can see magnets everywhere-in your fridge, in hooks to hold something, in your shower curtain, in your audio speakers, etc. They are usually black or dark gray in color, but the surface may be painted in any bright. Magnets tend to become weaker after sometimes if their poles are left free. This is called self-demagnetization. To avoid self-demagnetization, the magnets are kept in pairs with two ends of the pieces of soft iron stripes called ‘keepers’ placed across them. It helps to complete the magnetic circuit so there are no free poles to lose their strength. For the care of magnets, you need to be concerned with:

(a) Mechanical Shock: The magnets are brittle. They will chip or crack or break easily when dropped onto a hard surface, allowed to smash together with another magnet, allowed to smash together with a piece of metal or struck with a hammer or other hard substance.

(b) Heat: As the temperature increases, the molecules that make up the magnetic material, with their poles all lined up, will start to wiggle and jiggle around, causing the strength of the magnet to decrease.

ASSIGNMENT     

OBJECTIVES:

1. Which of these can be used to demonstrate the magnetic field pattern around a bar magnet?

A. Ball bearings B. Charcoal C. Galvanometer D. Iron fillings E. Magnetic shield

2. Which of the following is a natural magnet? A. Aluminum B. Iron C. Lead D. Loadstone E. Nickel

3. Magnetic force can be felt around A. copper B. iron C. lodestone D. nickel E. steel

4. Loadstone is an oxide of A. coal B. lead C. iron D. kaolin E. tin

5. Which of the following is not a magnetic material? A. Cobalt B. Iron C. Nickel D. Plastic E. Steel

THEORY:

1. Differentiate between a magnet and magnetism.

2. List three naturally occurring magnets.

3. State the laws of magnetism.

4. List the poles of a magnet and explain magnetic line of force.

5. How would you care for a magnet?