MAGNETISM

I.General Properties of magnets A. They have polarity – A north and a south pole A. They have polarity – A north and a south pole B. Like poles repel, unlike poles attract B. Like poles repel, unlike poles attract C. Compass is a small, suspended, needle-shaped magnet. Compass needles point toward the magnetic north pole of the earth. C. Compass is a small, suspended, needle-shaped magnet. Compass needles point toward the magnetic north pole of the earth.

D. Cobalt and nickel are important magnetic substances 1. Permanent magnets (retain magnetism for a long time) made from alloys of these metals. 1. Permanent magnets (retain magnetism for a long time) made from alloys of these metals. 2. ALNICO 2. ALNICO E.Iron, cobalt and nickel may be magnetized by induction.

1. When iron touches a permanent magnet it becomes magnetic when in contact. 1. When iron touches a permanent magnet it becomes magnetic when in contact. F. Why do certain substances become magnetic?

II. Magnetic Fields A. Magnetic field lines are called flux lines A. Magnetic field lines are called flux lines B. Outside the magnet they run from the north pole to the south pole B. Outside the magnet they run from the north pole to the south pole C. Inside the magnet they run from south pole to north pole always forming a closed loop. C. Inside the magnet they run from south pole to north pole always forming a closed loop.

D. The direction of the magnetic field lines is the direction the N-Pole of a compass points when placed in the magnetic field D. The direction of the magnetic field lines is the direction the N-Pole of a compass points when placed in the magnetic field

IV. Electromagnetism A. Discovered by Hans Christian Oersted in 1820 A. Discovered by Hans Christian Oersted in 1820 B. When an electric current moves through a wire a magnetic field is produced. B. When an electric current moves through a wire a magnetic field is produced. 1. The strength of the magnetic field varies directly with the current through the wire and inversely with the distance from the wire. 1. The strength of the magnetic field varies directly with the current through the wire and inversely with the distance from the wire.

C.Electromagnets: 1. Made by wrapping wire around an iron core 1. Made by wrapping wire around an iron core 2. Note that the magnetic field is strongest inside the coil and uniform 2. Note that the magnetic field is strongest inside the coil and uniform

3. The Strength of the magnet depends on amount of current, the number of turns and the nature of the core. a. More current – more induction a. More current – more induction b. More turns- more induction b. More turns- more induction c. A ferromagnetic core (iron) placed inside the coil will increase the induction c. A ferromagnetic core (iron) placed inside the coil will increase the induction

VI.Electromagnetic Induction A. Michael Faraday discovered in 1831 that moving a wire across an magnetic field induces an electric current in the wire. A. Michael Faraday discovered in 1831 that moving a wire across an magnetic field induces an electric current in the wire. B. For a current to be produced, either the conductor must move through the field or the field can move past the conductor. At right angles B. For a current to be produced, either the conductor must move through the field or the field can move past the conductor. At right angles C. Currents produced in this way is called electromagnetic induction C. Currents produced in this way is called electromagnetic induction