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36.1 – magnetic poles

36.1 – magnetic poles. Always have two poles 1 pole seeks north, other seeks south Like poles  repulsive Unlike  attractive All magnets have two poles. 36.2 – magnetic fields. Direction of force when magnet is placed in someone else’s location Usually a compass

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36.1 – magnetic poles

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  1. 36.1 – magnetic poles • Always have two poles • 1 pole seeks north, other seeks south • Like poles  repulsive • Unlike  attractive • All magnets have two poles

  2. 36.2 – magnetic fields • Direction of force when magnet is placed in someone else’s location • Usually a compass • Extends from pole to pole, N  S • Iron (or other magnets) tend to line up parallel to field • Recall how electric fields were generated

  3. 36.3 – the nature of a magnetic field • Moving electric charges generate a magnetic field • Stationary = only electric fields • Atoms have moving electrons  magnetism • Somehow (?) spinning electrons create magnetism • Materials in which spins “coordinate” can become magnetic – Fe, Ni, Co

  4. 36.4 – Magnetic domains • Clusters of aligned atoms – have same relative magnetic field • Presence of magnetism near Fe “forces” an alignment – creating temporary magnet • Permanent magnet – domains stay in place after field is removed

  5. 36.6 – magnetic forces on moving charged particles • Moving charges experience forces w/I magnetic fields • Greatest when perpendicular, zero when parallel • Direction of force is perpend. to field & velocity of charge • Found by using right hand rule • Particles can be steered by mag. Fields • Old style TV’s & Earth

  6. 36.5 – electric currents & magnetic fields • Since moving charges produce magnetism so do electric currents • Field is not radial • Field forms circles around conductor

  7. If wire forms a loop, the field lines are concentrated in the center of loop • Doubling loops – double field strength • Many loops form an electromagnet • Iron placed inside loop coils intensifies magnetic field • Most powerful electromagnets – superconducting

  8. 36.7 – magnetic forces on current carrying wires • Current (moving charges) also causes a deflection (force) on wires • Again perpendicular to field & direction of current • Parallel wire with field = no deflection • Symmetry: current deflects magnetic compass & magnets deflect current carrying wires

  9. 36.8 – meters to motors Galvanometers • Magnetic needle inside loops of wire indicates current – galvanometer • The more coils – the more sensitive • Can be made into a ammeter or voltmeter

  10. Electric motors • Electric motor = galvanometer made to change current direction with every half rotation • Current flow in opposite directions causes forces in opposite directions

  11. 36.9 – earth’s magnetic field • The earth acts as a giant magnet • Geographic/Magnetic poles do not line up • Difference between = magnetic declination • “current” theory – liquid inside (core) is flowing creating magnetism • Magnetism has “switched” (reversed) many times in the past

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