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# Cause magnetic fields t moving charges or current in

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Unformatted text preview: 2013 7   Magnetic field lines always come in LOOPS.   This is very different from electric field lines which end or begin at charge objects.   Magnetic monopoles have never been observed.   This would be something like an electric charge that emits or absorbs magnetic field lines. Physics 2B - Summer Session 2 - C. Palmer August 21, 2013 8   Magnetic field lines always come in LOOPS.   Magnetic monopoles have never been observed.   Consequence:   Through any CLOSED surface magnetic field lines go in and out. ∫ B ⋅ dA = 0 Physics 2B - Summer Session 2 - C. Palmer August 21, 2013 9   Magnetic field lines always come in LOOPS.   Magnetic monopoles have never been observed.   Consequence:   Through any CLOSED surface magnetic field lines go in and out. ∫ B ⋅ dA = 0   This is our 2nd of 4 Maxwell equations.   Gauss’s Law was the 1st Physics 2B - Summer Session 2 - C. Palmer August 21, 2013 10   Given that we know the field, we can determine the force.   Compared to relationship between electric force and electric field FE = qE the magnetic force and field have a more interesting relationship. FB = q v × B ( )   How do we interpret this? Physics 2B - Summer Session 2 - C. Palmer August 21, 2013 11   RHR is a tool for understanding the direction of the result from a cross product.   In our case, we are going to use this rule to determine the direction of the force resulting from a magnetic field. FB = q v × B ( ) FMag qv B Physics 2B - Summer Session 2 - C. Palmer August 21, 2013 12 Which direction is the Magnetic force going to be on this positive charge? FMag A)  Left B)  Right C)  Up qv + B D)  Down Physics 2B - Summer Session 2 - C. Palmer August 21, 2013 13 Which direction is the Magnetic force going to be on this positive charge? FMag A)  Left B)  Right C)  Up qv + B D)  Down Physics 2B - Summer Session 2 - C. Palmer August 21, 2013 14 What happens when the charge is NEGATIVE? Which direction is the Magnetic force going to be on this NEGATIVE charge? FMag A)  Left B)  Right qv - B C)  Up D)  Down Physics 2B - Summer Session 2 - C. Palmer August 21, 2013 15 What happens when the charge is NEGATIVE? Which direction is the Magnetic force going to be on this NEGATIVE charge? FMag A)  Left B)  Right qv - B C)  Up D)  Down Physics 2B - Summer Session 2 - C. Palmer August 21, 2013 16   Now the magnitude needs to be understood. FB = q FB = q ( v×B ⇒ v B sin θ )   Where θ is the angle between v and B Physics 2B - Summer Session 2 - C. Palmer August 21, 2013 17 There is a uniform magnetic field going out of the page with strength, B0, in the z direction. An electron is moving w...
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## This note was uploaded on 09/10/2013 for the course PHYS 2B 2b taught by Professor Hirsch during the Summer '10 term at UCSD.

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