21 magneticMaterials

21 magneticMaterials - Craig Ogilvie Craig Ogilvie 11...

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Unformatted text preview: Craig Ogilvie Craig Ogilvie 11 Summary Lecture 20 Calculating Fields, E and B r r q E ˆ 4 1 2 πε = Coulomb Law ˆ 4 2 r r v q B × = π μ Biot-Savart Law can always use, but requires superposition ε encl q A d E = ⋅ ∫ ∫ Gauss Law i d intercepte μ ∫ = ⋅ l d B Ampere’s Law always true useful when charge, current distributions are symmetric Craig Ogilvie Craig Ogilvie 22 Goals For Today § Complete our work on the sources of B-fields – Why some materials make magnets § Quantitative: strength of electromagnets Craig Ogilvie Craig Ogilvie 33 Question: Magnetic Moment, one round 1 2 3 4 0% 0% 0% 0% § magnetic moment μ = i*Area for a loop i is counter-clockwise, what is the direction of μ ? Right hand fingers in direction of i thumb direction of μ 1. 1 2. 2 3. 3 4. 4 0 of 300 Craig Ogilvie Craig Ogilvie 44 Force Exerted on Current Loop § In a uniform B-field, force on loop = 0 when μ is opposite to f8e5 B, force repels from region stronger field when μ is parallel to f8e5 B, force is towards region of stronger field dF perpendicular to B dF has a component towards bar magnet in non-uniform B-field current loop experiences a net force Craig Ogilvie Craig Ogilvie 55 Some Materials Attracted to Magnets § Electrons bound to nucleus, orbitals: loops of current – Orbitals have a magnetic moment § Atoms can have a net magnetic moment § Place these atoms inside a B-field – magnetic moments rotate parallel to the B-field (torque) – Once lined up, attracted to regions of strong B-field non-uniform B-field dF perpendicular to B Craig Ogilvie...
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This note was uploaded on 09/20/2011 for the course PHYS 222 taught by Professor Johnson during the Spring '07 term at Iowa State.

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21 magneticMaterials - Craig Ogilvie Craig Ogilvie 11...

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