MAGNETISM GRADE 10 CAPS SUTHERLAND HIGH SCHOOL PHYSICAL SCIENCE R. BASSON

Transcription

1 MAGNETISM GRADE 10 CAPS SUTHERLAND HIGH SCHOOL PHYSICAL SCIENCE R. BASSON

2 THE BEGINNING Greek shepherd found that the nails in his shoes and the metal tip in his staff was attracted to a black rock. This black rock was later found to have a natural magnetic substance (iron oxide). MAGNETITE TB. pg 87

3 USES OF MAGNETISM Magnets are used to: Hold objects together Separate objects Hoist objects Used in appliances telephones, loudspeakers, doorbells etc. Computer hard drives store information in magnetic patterns. Bank cards black strip to identify card holders. TB. pg 87

4 TB. pg 88 MAGNETIC POLES These are the ends of a magnet. The pole at the end of a magnet that points in a northerly direction is the north pole. The pole at the end of a magnet that points in a southerly direction is the south pole. The straight line joining the two poles magnetic axis.

5 FORCES OF MAGNETS Magnetic forces are non-contact forces exerts a force without touching. The effect of the magnetic force is experienced all around the magnet but is the strongest at its poles. Unlike (different) poles attract each other. Like (same) poles repel each other. TB. pg 88

6 MAGNETIC AND NON-MAGNETIC MATERIALS Magnetic materials are those that can be magnetized (become a magnet i.e. have a north pole and a south pole) in the presence of a magnet and are thus strongly attracted to a magnet. Those that can become magnetized are called ferromagnetic materials. Examples: Iron, Nickel and Cobalt and their alloys. Non-ferromagnetic materials are those that are not attracted to magnets. E.g. aluminium and non-metals TB. pg 88

7 High concentration of fillings around the poles indicate that the magnetic field is strongest at the poles. TB. pg 89 MAGNETIC FIELDS Any area in space in which a magnetic substance will experience a force. Invisible but effects can be observed by making use of iron fillings to map out the magnetic field around a bar magnet. Fields have magnitude and direction (vectors).

8 TB. pg 89 OTHER FIELDS ELECTRICAL GRAVITATIONAL An area or space where an electrical charge will experience an electrical force. NB! An area or space where a mass will experience a gravitational force.

9 Magnetic Field Electrical fields Gravitational Field Vector/scalar Vector Vector Vector Direction From N to S The direction that a positive charge would move. Force experienced by Ferromagnetic substances Charges Towards centre of mass Masses Visible/Invisible Invisible Invisible Invisible Exists because of Magnet with a N pole and a S pole Positive or negative Matter that has mass. TB. pg 89

10 TB. pg 90 DIRECTION OF A MAGNETIC FIELD Always from N pole to the S pole. Magnetic field lines have the following properties: Continuous Imaginary 3 dimensional Run from the north pole to the south pole. Never cross or touch each other. Are more concentrated at points where the field is strongest

11 TB. pg 92 THE MAGNETIC FIELD AROUND A BAR MAGNET Lines move from the north pole to the south pole. Field lines between two attracting poles. Field lines between two repelling poles.

12 TB. pg 92 THEORY OF MAGNETISM When a bar magnet is broken into smaller pieces, every piece becomes a magnet with a N pole and a S pole. These small magnets can be broken into smaller magnets. definition

13 THEORY OF MAGNETISM The smallest magnet is inside the atom because of the moving electrons. Moving electrons induce magnetic fields. In substances that are non-magnetic, these magnetic fields are random and in all directions. TB. pg 92

14 THEORY OF MAGNETISM In unmagnetised ferromagnetic materials, atoms are grouped together in magnetic domains. The domains each have magnetic fields that point in different directions. A domain is microscopic and consists of millions of atoms. When an object becomes magnetized, all the magnetic fields align in one direction. This results in a net magnetic field. TB. pg 93

15 TB. pg 93 ELECTROMAGNETS AND PERMANENT MAGNETS Hard ferromagnetic substances Domains are not easily aligned. Domains remain aligned for a long time. Permanent magnets Soft ferromagnetic substances Easily magnetized Lose magnetism quickly Electromagnets

16 The earth s magnetic field The earth has it s own magnetic field. The earth does have a core of iron and nickel but the temperature is too high for it to be magnetized. It s like the earth is made of a huge bar magnet. The magnetic north pole is the geographic south pole and the magnetic south pole is the geographic north pole. A freely rotating compass needle will point to the magnetic north pole of the earth. TB. pg 94

17 TB. pg 94 The angle of declination This is the angle between where the compass needle points and the true north. This differs from place to place and can change over time. Example: The angle of declination is 7 at some places on earth. The means that the angle between the magnetic north pole and the true north pole is 7.

18 IMPORTANCE OF EARTH MAGNETIC FIELD The area above the atmosphere is influenced by the earths magnetic field. This area is called the magnetosphere. This magnetosphere deflects solar winds away from the earth and prevents them from reaching earth. Solar winds are a flow of radioactive and charged particles. Without the magnetosphere, the earth would be damaged by solar winds and no life on earth would be possible. TB. pg 95

19 TB. pg 95 IMPORTANCE OF EARTH MAGNETIC FIELD Sometimes, large quantities of the high energy particles from the sun do enter the earths atmosphere and move along the magnetic field lines towards the poles. The charged particles collide with air particles and light is emitted causing a beautiful aurora. (Northern lights and southern lights)

20 TB. pg 95 IMPORTANCE OF EARTH MAGNETIC FIELD The earths magnetic field helps migrating birds to chart their flight during the migration season.

21 REVISION

22 COMMON QUESTIONS

23 MAGNETIC?

24 HOMEWORK EXERCISE 9 PG