lecture13

lecture13 - L ecture 13 M agnets Magnetic Fields M agnetic...

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Lecture 13: Magnets / Magnetic Fields Magnetic Force Charged Particle Motion

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Physics Concept Components Learning Outcome Magnetic Force and Field Charged particle motion Induced EMF Faraday’s Law Lenz’s Law Self inductance Ampere’s Law Mutual inductance Evaluate the force on and simple motion of a charged object in a magnetic field Predict the effects of a varying magnetic field on conductors (especially wires). Compute algebraic expressions for magnetic fields using Ampere’s Law August 21, 2013 2 Physics 2B -­‐ Summer Session 2 -­‐ C. Palmer
In the 1820s, experiments showed that magnetic fields could induce current in wires. A bit later experiments showed that magnetic fields could be created by electric currents. The earth’s magnetic field is made from the hot, dense, molten, Iron core. IT IS ROTATING! The rotation produces the magnetic field. We are very lucky to the earth’s magnetic field. http://www.youtube.com/watch?v=yEYy_nVC4L0 August 21, 2013 3 Physics 2B -­‐ Summer Session 2 -­‐ C. Palmer

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Electrostatics Magnetism +/-­‐ charges North/South poles Like charges repel / Opposite charges attract Like poles repel / Opposite poles attract Can separate +/-­‐ charges CANNOT separate North/ South poles Field lines start/stop with charges Field lines are in loops Field created by charge Field created by moving charge Acts at a distance Acts at a distance August 21, 2013 4 Physics 2B -­‐ Summer Session 2 -­‐ C. Palmer
Best way to learn about/use the magnetic force is to focus on the field. We denote the magnetic field with SI Units: Telsa, T The magnetic field is created in an analogous fashion to the electric field. Not with charge With MOVING charge August 21, 2013 5 Physics 2B -­‐ Summer Session 2 -­‐ C. Palmer B B [ ] = T = N C m s ( )

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A field “creates a ‘condition’ in space” such that when you put a charged object in it, the charged object “feels a force”. -Richard Feynman It is a vector proportional to force on a test charge. August 21, 2013 6 Physics 2B -­‐ Summer Session 2 -­‐ C. Palmer There Exists Charged Stuff [C] + + -­‐ -­‐ -­‐ + + -­‐ -­‐ -­‐ Charged Stuff Creates a Field [N/C] Other Charged Stuff Feels the Field [N] -­‐ F Elec = q 0 E
Best way to learn about/use the magnetic force is to focus on the field. Moving charges/Current [A] Cause magnetic fields [T] MOVING charges or current in the field feel a force [N] If they move in the right direction. August 21, 2013 7 Physics 2B -­‐ Summer Session 2 -­‐ C. Palmer + + + + The field is visualized with x’s and dots LIKE ARROWS Into the page (back of arrow) Out of the page (front of arrow) F B = q 0 v × B

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Magnetic field lines always come in LOOPS.
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