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
What does a magnet do ? It can deflect a compass needle. N
S
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’.
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.
What is the source of magnetism ? What makes a magnet ? Current flowing through wires. This can pick up paper clips !? How ? It’s ‘magnetic’. current loop with current i
N
A bar magnet S
What’s the difference between a current loop and a bar magnet ?
current loop with current i
N
A bar magnet S
They can produce the same magnetic field ! Magnetism is intimately related to flowing currents.
3 Methods of Magnetic Levitation 1. Magnets on Track and Train – Repulsion produces levitation but equilibrium is UNSTABLE. 4. AC Levitation – AC Electromagnet on Train, on Metal Tracks produces levitation but energy immediately decays away. 8. 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