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. V max = 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. 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’. NS

What’s in a Magnet ? What if you cut it up ? NS 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 ? This can pick up paper clips !? How ? It’s ‘magnetic’. Current flowing through wires. current loop with current i N S A bar magnet

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.

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