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Magnets make speakers work

Magnets make speakers work. The force between the permanent magnet and the voice coil moves the speaker cone. N. N. N. N. N. N. S. S. S. S. S. S. N. S. S. N. Maglev trains.

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Magnets make speakers work

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  1. Magnets make speakers work The force between the permanent magnet and the voice coil moves the speaker cone

  2. N N N N N N S S S S S S N S S N Maglev trains Alternating current switches the polarity of the guidance coils in the walls. This continually propels the train along

  3. Maglev trains World record for a maglev train 581 km/h (361 mph) in Yamanashi prefecture (Japan)

  4. Wire with current = magnet • If you pass current through a wire, the wire has a magnetic field → can prove with a compass A wire with current flowing through it becomes a magnet (an “electromagnet”) • Anything that conducts electricity (therefore usually metals) can be an electromagnet

  5. 1777 - 1851 Hans Christian Oersted • Electromagnetism was discovered accidentally in 1820 • While setting up equipment, Oersted noticed a compass needle deflected when he switched the current on and off through a nearby wire

  6. Right-Hand Rule #2 • How do you determine the direction of the magnetic field around the wire? Kinetic Books • Wrap your hand around the wire so that your thumb points in the direction of the (conventional) current • Your four fingers will curl around the wire in the direction of the magnetic field

  7. Magnetic Field around a Current-Carrying Wire Strength of magnetic field around a wire • Increases with amount of current • Decreases with distance from wire B = magnetic field μo = permeability of free space = 4πx 10-7 T·m/A I = current R = distance from center of wire

  8. I = 5 A Example A long, straight wire carries a current of 5 A. What is the strength and direction of the magnetic field 4 cm from the wire? P Field points into screen at point P

  9. Strengthen an electromagnet S N • more Current • more Coils per meter • iron Core

  10. Nail or “core” Electromagnets • Core needs to be ferromagnetic (have domains) • The magnetic field of the loops aligns the domains of the nail (nail gets magnetized) • The magnetic field is now stronger than that of the coil’s magnetic field alone Coil

  11. Field lines concentrated in center of core Looping a wire strengthens the magnetic field of the wire current

  12. Where are the north and south poles for a loop of wire? Use RHR #2

  13. S N More loops = stronger magnetic field Use RHR #2 to find the north and south poles But if you reverse the direction of the current in the loops, the poles will switch sides

  14. The field lines inside the coils align the domains of the iron nail in the core N S

  15. Permanent Magnet Electromagnet Electromagnets and permanent magnets have similar fields N S N S

  16. Magnetic Resonance Imaging • Patient lies in the center of a large solenoid • Magnetic field inside solenoid = 1 to 2 tesla (up to 40,000x stronger than Earth’s B field)

  17. Magnetic Resonance Imaging

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