1. Magnetism Chapter 22 Page 439-454

2. Properties of Magnets • Magnetic material- has the ability to exert forces on magnets other magnetic materials. • Permanent magnet-always keep their magnetic charge some examples are refrigerator magnets, magnets and horseshoe magnets

3. Properties of magnets • Every magnet has a south and a north pole

4. Magnetic force • Like poles repel each other and unlike poles attract each other. • Plastic, wood and most insulating materials are transparent to magnetic forces. • Magnets can drag other magnets through transparent objects

5. Magnetic forces • They are relatively easy to create and can be very strong. • There are many ways to make magnets with forces strong enough to lift a car or even a moving train.

6. Force between two magnets • The strength of the force between magnets depends on the distance between them. • The total force between the magnets is the sum of all four magnetic poles. • When magnets are separated by more than a few times their size. The attract and repel forces tend to cancel each other out. • The total force decreases rapidly as the separation increases.

7. Force between two magnets • Mathematically the force between two magnets decreases with distance much more rapidly than the inverse square law. • Torque can occur when two magnets are close together because of the poles.

8. Magnetic field • Two magnets can make a magnetic field • Magnetic field lines when you draw the arrows around the magnets and around the source magnet. • When you have magnetic field lines the closer they are the stronger the field. • MRI work is based on magnetic stimulation of atoms in your body

9. Source of Magnetism • The source of magnetism is due to the electrons inside the magnet. • Diamagnetic magnets you often have an arrangement of electrons in order to get cancellation of magnetic fields. • Paramagnetic materials become weakly magnetic

10. Ferromagnetism • Examples of ferromagnetic materials include nickel, cobalt and iron. • They make magnetic domains and not paramagnets or diamagnets. • Iron, iron shavings and paper clips are affected more from ferromagnets. • Domains can attract either pole.

11. Properties of ferromagnetic materials • You make permanent magnets by stroking ferromagnets domains. • Hard magnets can make good permanent magnets. • Neodymium and steel make good hard magnets and therefore good permanent magnets.

12. Properties of ferromagnetic materials • Soft magnets are magnets that lose their magnetism quickly. • Like from bar magnets • If a magnet is vibrated or repeatedly struck a magnet can be demagnetized. • High temperatures can do the same thing

13. Discovering and using magnetism • Lodestone and magnetite were discovered in 500 B C and they are naturally occurring magnets. Led to use of compasses. • 220 BC the compass was discovered in China. • Was called south pointer. • It was balanced on a plate and the handle was aligned with magnetic south

14. Discovering and using magnetism • 1088 AD the Chinese were using a small compass. • Chinese sailors could go to Saudi Arabia ok • 100 years later Europe started using it • 1400 AD Chinese were going to Africa and this led to many interactions among cultures.

15. Working of a compass • A compass is a magnet that is free to spin. • The north pole of a compass needle always points toward the south pole of a permanent magnet. • The north pole and south pole of a compass was decided before people understand magnets.

16. Working of a compass • The geographical north pole are at the points at which the Earth’s axis of rotation intersects th planet surface.

17. Source of the Earth’s Magnetism • You cannot trust a compass to point north if a magnet is around. • Gauss is a unit used to measure the strength of a magnetic field. • Gauss increases at you get closer to the core of the earth it is .5 at the surface of the earth. • The outer core has a molten consistently that gives the core a magnetic field like an electromagnet

18. Source of the Earth’s Magnetism • The north and south magnetic poles has switched places. • Every 500,000 years and it has been 750,000 years since the last one so we are due a reverse of magnetic polarity. • The Earth is lising 7% of its strength every 100 years. So reversal could occur in next 2000 years.

19. Source of the Earth’s Magnetism • The location of the Earth’s magnetic pole is always changing. • Currently the magnetic south pole is licacted about 1000 km (600 miles) from the geographic north pole

20. Magnetic declination • Compass will not point directly to the geographic north • Is measured in degrees and is indicated on topographical maps • Depending on where you are the compass will point either east or west of north • Most maps will give you the declination such as on page 450