Magnetic Demonstations Magnetic Interactions FerroMagnets very strong attraction

Magnetic Demonstations Magnetic Interactions • Ferro-Magnets very strong attraction – Examples: Iron, steel, nickel. • Eddy-Current weak damping force – Examples: any conductor • Dia-magnets very weak repulsion – Examples: water droplet & levitating frog – Much stronger in Superconductors Lines of Magnetic Force Ferro. Fluid • Consists of Ultra-small ferro -magnetic particles • Particles tend to stack along magnetic field lines • Applications: – Adjustable shock absorbers – Friction reduction Particles stack in magnetic field. Ferro. Tec Corporation Water droplet and frog levitating in a very strong (10 – 20 Tesla magnet. (10 T is 200, 000 x the field of the earth. ) Eddy Current Damping • Magnet induces eddy-currents in metals (conductors). • Eddy-current generate magnetic fields that repel and slow (oppose) the magnet. • Effect stronger for: – Magnet closer to conductor. – Thicker conductor. – Better conductor: Copper (Cu) r. Cu = 1. 7 x 10 -6 W-cm Aluminum (Al) r. Al = 1. 6 x r. Cu Stainless Steel r = 35 x r. Cu Forces act to slow magnet Ferro fluid has ultra small-magnetic particles suspended in a fluid (like fat globules in milk) 85% carrier, 10% surfactant, 5% magnetic solid Eddy-current generate magnetic fields that repel and slow (oppose) the magnet. Solid vane stops quickly. Vane with loops stops. Vane with teeth stops slowly.