Magnetic Fields

1. Magnetic Fields Chapter 24

2. 24.1 Magnets: Permanent & Temporary • Electric generators • Television sets • Cathode-ray displays • Computer hard drives • Compass

3. General Properties of Magnets • Polarized-magnets are polarized. They have two distinct and opposite ends. • North pole and South pole • Like electric charges, likes repel and opposites attract • However, charges can be separated magnetic poles cannot.

4. The Earth itself is a large magnet. • The north end of a compass needle (a magnet) points to the geographic north pole. • The geographic north pole is the magnetic south pole

6. How Do Magnets Affect Other Material? • A magnet can cause another metal to become polarized and have magnet properties.

7. Permanent Magnets • Because of the microscopic nature of the material it keeps the magnetic properties • ALNICO V-a permanent magnet alloy aluminum, nickel, and cobalt • Rare earth elements neodymium and gadolinium produce very strong permanent magnets for their size

8. Magnetic Fields Around Permanent Magnets • Magnetic forces can be describe by the existence of a field around the magnet • Much like gravitational and electric fields • Can be non-contact forces • Magnetic fields are vector quantities that exist in a region in space where a magnetic force occurs.

10. Magnetic Field Lines • Magnetic field lines are imaginary lines used to help visualize a magnetic field. • Direction of field lines are defined as the direction that a compass points when placed in the magnetic field. • Outside the magnet field lines leave the magnet from the north pole and end the south • Inside the magnet from south to north to form a closed loop.

11. Magnetic Flux • The number of field lines passing through a surface is the magnetic flux • The flux per unit area is proportional to the strength of the magnetic field.

12. Electromagnetism • In 1820, Danish physicist Hans Christian Oersted experimented with electric currents in wires. • Found that when a current was in a wire a compass needle rotated until it was perpendicular to the wire. • If the compass needle rotated it must have been because of a magnetic field.

13. Circular line indicate that magnetic field lines around a current carrying wire for closed loop in the same way that field lines about a permanent magnet for closed loops.

15. First Right-Hand Rule • A method to determine the direction of a magnetic field relative to the direction of conventional current • Pretend to hold the wire with your right hand • Point you thumb in the direction of conventional current • Your fingers point in the direction of the magnetic field.

17. Magnetic Field Near a Coil • A long coil of wire consisting of many loops is called a solenoid. • The field of each loop adds to the fields of the other loops and creates a greater total field strength.

19. Second Right-Hand Rule • A method used to determine the direction of the field produced by an electromagnet relative to the flow of conventional current. • Curl your right hand fingers around the loops in the direction of the conventional current • Your thumb points toward the north pole of the electromagnet

21. A Microscopic Picture of Magnetic Materials • Electrons in an atom acts like a tiny electromagnet • Domain is when the magnetic fields of the electrons in a group of neighboring atoms are all aligned in the same direction • When a piece of iron is not in a magnetic field the domains point in random directions and their magnetic fields cancel each other out.

22. In the case of a temporary magnetic and external magnetic field aligns the domains and when the external magnetic field is removed the domains return to their random arrangement • In a permanent magnet the iron keeps the domains aligned after the external magnet is removed.