2. Magnetic Fields A PowerPoint Presentation by Paul E. Tippens, Professor of Physics Southern Polytechnic State University A PowerPoint Presentation by Paul E. Tippens, Professor of Physics Southern Polytechnic State University © 2007

3. Objectives: After completing this module, you should be able to: Define the magnetic field, discussing magnetic polesDefine the magnetic field, discussing magnetic poles

4. Magnetism Since ancient times, certain materials, called magnets, have been known to have the property of attracting tiny pieces of metal. This attractive property is called magnetism. N S Bar Magnet N S

5. Magnetism The domain theory is a simple model of magnetism which states that all materials are made up of tiny regions called domains. The domains behave like magnets. Random distribution=no magnetic effect Domains aligned=magnetized

6. Magnetic Poles The strength of a magnet is concentrated at the ends, called north and south “poles” of the magnet. A suspended magnet: N-seeking end and S-seeking end are N and S poles. NS N E W S N Compass Bar magnet S N Iron filings

7. Magnetic Attraction-Repulsion N S N N S S NS NS Magnetic Forces: Like Poles Repel Unlike Poles Attract

8. Magnetic Field Lines NS We can describe magnetic field lines by imagining a tiny compass placed at nearby points. The direction of the magnetic field B at any point is the same as the direction indicated by this compass. Field B is strong where lines are dense and weak where lines are sparse.

9. Magnetic Field Lines The field lines follow the needle on the compass

10. Field Lines Between Magnets NS NN Unlike poles Like poles Leave N and enter S Attraction Repulsion