24-1 Magnets: permanent & temporary

1. 24-1 Magnets: permanent & temporary

2. General Properties • Hang the bar magnet from the thread, observe what happens……. • Positions itself in the N-S directions - magnet is polarized • Has two ends – North seeking and South seeking • A compass is a small magnet free to turn

3. General Properties • Observe what happens when another magnet is brought to the different sides of the magnet • The two N poles repel as the two S poles • N and S pole attract • All magnets have two singular poles or Monopoles • When magnet is broken in half, magnets orient themselves in a N & S direction

4. Simple Magnets • Touch a magnet to a piece of metal (iron nail) and try to pick up paper clips along the nail • Nail has become polarized (temporarily) • Either end of a magnet will attach to a metal

5. Permanent Magnets • Made of ALNICO V • Aluminum – Nickel – Cobalt – and other rare earth elements

6. Magnetic Field • Magnets are a long range force • Invisible “lines” surround the magnet showing the magnetic field • Number of magnetic lines is magnetic flux • # of lines is proportional to strength • Concentrated at the poles • Lines flow out of the N and into the S in closed loops

7. Electromagnetism • Electric currents through a wire create a magnetic field perpendicular to the current • First Right hand Rule • Direction of current  Thumb • Direction of magnetic field  Fingers coiled

8. Magnetic Field near a Coil • A wire looped several times to form a coil and a current is allowed to flow, the field around all the loops is always in the same direction • Solenoid • Long coil wire consisting of many loops

9. Magnetic Field near a Coil • When there is an electric current in a coil wire, the field acts like a permanent magnet • Electromagnet • Strength of the field is proportional to the current in the coil • Increasing the number of loops increases the strength

10. Electromagnet • Strength can also be increased by adding an iron rod inside the coil • Field will magnetize the rod • Second right hand rule • Direction of magnetic field produced by an electromagnet • Curl fingers around loops in the direction of the current • Thumb is the North pole of the magnet

11. Magnetic Domains • Each electron in an atom acts like a tiny electromagnet  generally in three magnetic elements • Iron, nickel, & cobalt • Groups of electrons are known as domains • Shown as arrows that are random in direction • Once a magnetic field is present, arrows aligned and become magnetized

12. Physics and Earth Science • Iron is found in the oceanic rocks as basalt • As ocean floor spreads, magma is released • Overtime, earth’s magnetic field has changed