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AP Physics B Chapter 20 Magnetism 20-1

AP Physics B Chapter 20 Magnetism 20-1. All magnets have 2 poles called north and south. Materials that show strong magnetic effects are said to be ferromagnetic. A magnetic field surrounds any magnet or conductor.

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AP Physics B Chapter 20 Magnetism 20-1

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  1. AP Physics B Chapter 20Magnetism 20-1 All magnets have 2 poles called north and south. Materials that show strong magnetic effects are said to be ferromagnetic. A magnetic field surrounds any magnet or conductor. Magnetic field lines point the same way a north magnetic compass would point at that location. (N to S) See pg. 589 diagrams.

  2. 20-1 Magnets and Magnetism (cont’d) • We difine the magnetic field, at any point as a vector, represented by the symbol B, pointing to the south pole. • The angular difference between true north and magnetic north, on Earth, is called magnetic declination. • The angle of dip is the result of the magnetic field not being tangent at all points.

  3. 20-2 Electric Currents that Produce Magnetism • Hans Christian Oersted found that when a compass needle is placed near an electric wire, it shows a magnetic field when current is flowing. • We use the right-hand-rule to determine the direction of current or magnetic field. • See pg 591 for diagrams.

  4. 20-3 Force on an Electric Current in a Magnetic Field; Definition of B • Magnets exert a force on a current carrying conductor. • Use another right hand rule for the force with moving electrons. • 1. Orient your rt. hand to point fingers with the conventional current. (+) • 2. …from this position, bend your fingers so they point in the direction of the field-lines. • 3. The extended thumb is the direction of the force on a wire.

  5. 20-3 Force on an Electric Current in a Magnetic Field; Definition of B • F=IlBsinq • If the current is perpendicular to the field q =90, then sinq=1 • The SI unit for magnetic field is the tesla (T). • Another common unit is the gauss (G) • G=10-4 T. • The earth’s magnetic field is about .5x10-4T. • See Example 20-1 and Example 20-2 p593/p594.

  6. 20-4 Force on an Electric Charge Moving in a Magnetic Field • F=qvBsinq • Obviously Fmax =qvB • The force is zero if the particle moves parallel, it is maximum when it moves perpandicular. • See pg 594 and pg 595 for conventions of representing 3d fields in 2d. • See Examples 20-3 and 20-4 p595 and p596

  7. P616 1-12 due BOP Monday

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