1. Magnetically Levitated Trains

2. Question:
Suppose you have a long bar magnet with a north pole at one end and a south pole at the other. If you break it in half, will the two new ends:
Attract
Repel
Neither

3. Observations About Maglev Trains
Ordinary trains rattle on their rails
Magnetic suspension would be nice and soft
Repelling magnets tend to fall off one another
Attracting magnets tend to leap at each other

4. Magnetic Poles Two types: north & south
Like poles repel, opposites attract
Forces consist of a matched pair
Forces increase with decreasing separation
Analogous to electric charges EXCEPT:
No isolated magnetic poles ever found!
Net pole on an object is always zero!
Demonstration: Two North Poles Repel, Two South Poles Repel, and Opposite Poles Attract

5. Question:
Suppose you have a long bar magnet with a north pole at one end and a south pole at the other. If you break it in half, will the two new ends:
Attract
Repel
Neither
Demonstration: Separate Two Magnets That Were Taped Together

6. Magnetic Fields
A magnetic field is a structure in space that pushes on magnetic pole
The magnitude of the field is proportional to the magnitude of the force on a test pole
The direction of the field is the direction of the force on a north test pole

7. Electromagnetism 1 Electric fields Magnetic fields
Push only on electric charges
Produced by electric charges
Can be produced by changing magnetism
Magnetic fields
Push only on magnetic poles
Produced by magnetic poles
Can be produced by changing electricity
Demonstration: Move a Magnet Past a Coil and Light a Lamp

8. Electromagnetism 2 Magnetism created by Electricity created by
Poles (but isolated poles don’t seem to exist)
Moving electric charges
Changing electric fields
Electricity created by
Charges
Moving magnetic poles
Changing magnetic fields

9. Current
Current measures the electric charge passing through a region per unit of time
Current is measured in coulombs/second or amperes (amps)
Electric fields cause currents to flow
Currents are magnetic
Demonstration: Electromagnet and Steel

10. Equilibrium Stable equilibrium Unstable equilibrium
Zero net force at equilibrium
Accelerates toward equilibrium when disturbed
Unstable equilibrium
accelerates away from equilibrium when disturbed
Neutral equilibrium
Zero net force at or near equilibrium
Demonstration: Stable Equilibrium on U-Track
Demonstration: Unstable Equilibrium on Inverted-U-Track.
Demonstration: Neutral Equilibrium on Flat Track
Demonstration: Two Magnets Repel but are Unstable.
Demonstration: Suspended Bearing.
Demonstration: Levitron Top.

11. Levitation & Stability
Unstable Levitation Schemes
Static permanent magnets
Stable Levitation Schemes
Permanent magnets and contact
Dynamic stabilization with permanent magnets
Electromagnets and Feedback
Demonstration: Newton's Folly.

12. Electromagnetic Induction
Changing magnetic field  electric field
Electric field in conductor  current
Current  magnetic field
Induced magnetic field opposes the original magnetic field change (Lenz’s law)
Demonstration: Leaping Ring and Electromagnet

13. Levitation & Stability
Unstable Levitation Schemes
Static permanent magnets
Stable Levitation Schemes
Permanent magnets and contact
Dynamic stabilization with permanent magnets
Electromagnets and Feedback
Alternating Current Levitation

14. Alternating Current Levitation

15. Levitation & Stability
Unstable Levitation Schemes
Static permanent magnets
Stable Levitation Schemes
Permanent magnets and contact
Dynamic stabilization with permanent magnets
Electromagnets and Feedback
Alternating Current Levitation
Electrodynamic Levitation

16. Electrodynamic Levitation
Demonstration: Eddy Current Pendulum.
Demonstration: Magnet Falling Through Copper Pipe.
Demonstration: Magnet Sliding in Copper/Plexiglass Track.
Demonstration: Magnet Floating above Spinning Aluminum Disk
Demonstration: Copper Coil in Liquid Nitrogen
Demonstration: Magnet Floating Above Superconductor