p240_ct16_f07 - Physics 240 Fall 2007 Lecture #16 Dr. Dave...

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Unformatted text preview: Physics 240 Fall 2007 Lecture #16 Dr. Dave Winn 2405 Randall Lab [email protected] Second exam next Thursday, November 1, 8:00-9:30 Chapters 24.4-28.4 Origins of magnetic fields • Electric fields emerge from positive charge sources and disappear into negative charge sinks • Magnetic fields come from: – Permanent magnets – Moving charges – Changing E fields • No magnetic charges (monopoles) exist – Magnetic field lines never end, they must be closed loops Oersted demonstration Two right hand rules! 1. Right hand rule for cross-products: fingers along first vector, curl towards second, thumb shows direction 2. Curled/straight rules in magnetism: thumb along straight element, fingers show curled direction • Examples of the first rule: – F = q v x B – F = i L x B • Examples of the second rule – Direction of magnetic moment for a loop – Field direction of current element X X • X Four conducting wires carry current into and out of the page as shown. What is the direction of the magnetic field at the center of this square? 1. 2. 3. 4. 5. The field there is zero Quantifying B from a current • To calculate the total E field, we used superposition: total field is the vector sum of the field from each small charge dq. • To calculate B field, we add up the vector sum of the B field from each little current element i*ds....
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This note was uploaded on 04/04/2008 for the course PHYSICS 240 taught by Professor Davewinn during the Fall '08 term at University of Michigan.

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p240_ct16_f07 - Physics 240 Fall 2007 Lecture #16 Dr. Dave...

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