1. MAGNETISM

2. What is the cause of magnetism? The motion of charges cause magnetism. Example: Currents, spinning electrons. Magnetic Field: A region where a moving charge can experience a magnetic force. The terms magnetism and magnetic field are synonymous with each other. An electromagnetic phenomenon where moving charges produce a magnetic field.

3. Types of Magnetism The magnetism exhibited by materials can be classified as diamagnetic, paramagnetic, or ferromagnetic.

4. Diamagnetic Materials All electrons are paired so there is no net magnetic field. In the presence of an extremely strong external magnetic field, the electron paths are slightly altered, causing a small repulsion of the material. Magnetic properties are lost after an external magnetic field is removed.

5. Paramagnetic Materials A few electrons are unpaired so there is a very weak magnetic field. In the presence of an extremely strong external magnetic field, the electron paths are slightly altered, causing a small attraction of the material. Magnetic properties are lost after an external magnetic field is removed.

6. Ferromagnetic Materials Many electrons are unpaired so there is a moderate magnetic field in various regions of the material called domains. A domain is a region with approximately 10 20 electrons, the size of approximately 1 mm 2. In the presence of an strong external magnetic field, the electron domains align resulting in a strong magnetic field within the material. Magnetic properties are retained long after the external magnetic field is removed. Iron, cobalt, and nickel are ferromagnetic.

7. Why aren’t all materials ferromagnetic? An electron pair. In most elements the electron pairs spin in opposite directions, cancelling the magnetic field produced by the other electron. Iron, Cobalt, and Nickel Which elements are ferromagnetic? There are many more unpaired electrons thus resulting, in a strengthened magnetic field. In ferromagnetic materials: Ex Iron Electron Spin

8. Domain: A region with approximately 10 20 electrons (approximately 1 mm 2 ). In magnetic materials, the magnetic fields in the domains are arbitrarily orientated causing the element to have a weak magnetic field. A magnet is created by subjecting a magnetic material to a strong external magnetic field causing the domains to become aligned. An external magnetic field. NS

9. NS Heat and/or sharp blows can cause the domains to become unaligned. An alloy ALNICO (Aluminum, Nickel, and Cobalt) will make a magnet permanent once the domains are aligned.

10. N S Magnetic field lines are imaginary lines to show the magnitude and direction of magnetic force. Magnetic field lines are always directed away from the north towards the south. There are always two poles to magnetic fields, north and south. SNSN S N The magnetic field is said to be north-seeking. North-seeking refers to the geographic north of the Earth. The direction of a magnetic field is the direction that a compass will point if placed in the magnetic field. The magnetic field lines always form closed loops (continuous).

11. S N Earth’s geographic north is near the magnetic south. Earth’s geographic south is near the magnetic north. Earth’s Magnetic Field

12. NSSN The magnetic field between equal strength unlike magnetic poles is uniform. N S NS NS Various Magnetic Field Line Orientations Magnetic Field Lines between two North Poles.

13. Magnetic Pole Force Law Like poles repel. Unlike poles attract

14. The magnetic field is denoted by the letter B. The SI unit for the magnetic field is measured in the unit called a Tesla (T). The Tesla is part of the MKS system of units The older unit used for the magnetic field was a Weber/m 2 ( Wb/m 2). 1 T = 1 Wb/m 2 A Tesla made up of the fundamental units of kg/As 2 which come from a (kg m/s 2 )/[(As)m/s] The magnetic field is a vector quantity. 1 T=10 4 Gauss A Gauss is the cgs measurement of a magnetic field. The Magnetic Field

15. To put magnetic strengths in perspective, here is a table of magnetic field strengths The Earths magnetic field, which deflects compass needles (measured at the N magnetic pole) 0.6 Gaus s A common iron magnet like those used to stick papers on a refrigerator 100 Gaus s The strongest fields achieved so far in the laboratory Sustained (steady) 4 X 10 5 Gauss The strongest fields achieved so far in the laboratory Ephemeral (made using explosives; lasts only milliseconds) 10 7 Gauss The maximum field observed on ordinary stars - 10 6 Gauss Typical magnetic field of radio pulsars (the ordinary, familiar kind of neutron star; (hundreds are known to astronomers) 10 12 Gauss Magnetars(soft gamma repeaters) 10 14 - 10 15 Gauss