Magnetism and magnetic levitation trains are discussed. There is some discussion of implementing maglev trains in parts of the US. Three methods of magnetic levitation are described: 1) Using magnets on the track and train results in repulsion and levitation but unstable equilibrium. 2) AC levitation uses an AC electromagnet on the train and metal tracks but energy decays quickly. 3) Dynamic levitation uses a magnet on the train and metal tracks, producing the least energy dissipation by allowing the train to move fast enough initially.

1. Magnetism and Magnetic Levitation Trains
Does the US have them ? How do they work ?
What do they have to offer ?
1. Japan and Germany have demo versions. Vmax = 350 mph.
2. There is some talk of maglev trains in Southern Calif,
Baltimore-DC, and in Virginia

2. What does a magnet do ? It can deflect a compass needle.
This can’t be explained by mechanical forces. Can electrostatic forces
explain this ?
• No, these forces are in the wrong direction and occur even if
the compass needle, magnet are Neutral !!!
So…we must postulate a new type of force, with new type of ‘charges’
(which we call poles). Let’s call this force ‘Magnetism’.
N S

3. What’s in a Magnet ? What if you cut it up ?
N S
You get many magnets with N, S poles !
Experimentally, no single magnetic poles have been seen!
Just dipoles.

4. What is the source of magnetism ? What makes a magnet ?
This can pick up paper clips !? How ? It’s ‘magnetic’.
Current flowing
through wires.
current loop with current i
N
S
A bar magnet

5. current loop with current i
N
S
A bar magnet
What’s the difference between a current loop and a bar magnet ?
They can produce the same magnetic field !
Magnetism is intimately related to flowing currents.

6. 3 Methods of Magnetic Levitation
1. Magnets on Track and Train – Repulsion produces levitation
but equilibrium is UNSTABLE.
2. AC Levitation – AC Electromagnet on Train, on Metal Tracks
produces levitation but energy immediately
decays away.
3. Dynamic Levitation – Magnet on Train, on Metal Tracks
produces least energy dissipation by allowing
the train to initially move fast enough.
See Class Discussion Notes on Electromagnetic Induction and
Lenz’s Law

7. 3 Methods of Magnetic Levitation
1. Magnets on Track and Train – Repulsion produces levitation
but equilibrium is UNSTABLE.
2. AC Levitation – AC Electromagnet on Train, on Metal Tracks
produces levitation but energy immediately
decays away.
3. Dynamic Levitation – Magnet on Train, on Metal Tracks
produces least energy dissipation by allowing
the train to initially move fast enough.
See Class Discussion Notes on Electromagnetic Induction and
Lenz’s Law