Lecture13_2011

Lecture13_2011 - PHYS 272: Matter and Interactions II -...

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Fall 2010 Prof. Yong Chen ( yongchen@purdue.edu ) Prof. Michael Manfra ( mmanfra@purdue.edu ) Lecture 10 Slide 1 PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http://www.physics.purdue.edu/academic_programs/courses/phys272/ PHYSICS 272 Lecture 12 Magnetic Fields [EMI 18.5-18.7]
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Fall 2010 Prof. Yong Chen ( yongchen@purdue.edu ) Prof. Michael Manfra ( mmanfra@purdue.edu ) Lecture 10 Slide 2 PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http://www.physics.purdue.edu/academic_programs/courses/phys272/ Conclusions: The magnitude of B depends on the amount of current A wire with no current produces no B B is perpendicular to the direction of current B under the wire is opposite to B over the wire Oersted effect: discovered in 1820 by H. Ch. Ørsted How does the field around a wire look like? The Magnetic Effects of Currents
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Fall 2010 Prof. Yong Chen ( yongchen@purdue.edu ) Prof. Michael Manfra ( mmanfra@purdue.edu ) Lecture 10 Slide 3 PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http://www.physics.purdue.edu/academic_programs/courses/phys272/ Principle of superposition: wire Earth net B B B + = What can you say about the magnitudes of B Earth and B wire ? What if B Earth were much larger than B wire ? The Magnetic Effects of Currents The moving electrons in a wire create a magnetic field
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Fall 2010 Prof. Yong Chen ( yongchen@purdue.edu ) Prof. Michael Manfra ( mmanfra@purdue.edu ) Lecture 10 Slide 4 PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http://www.physics.purdue.edu/academic_programs/courses/phys272/ A current-carrying wire is oriented N-S and laid on top of a compass. The compass needle points 27 o west. What is the magnitude and direction of the magnetic field created by the wire B wire if the magnetic field of Earth is B Earth = 2 × 10 -5 T (tesla). wire Earth net B B B + = θ tan Earth wire B B = 27 tan 10 2 5 × × = - T wire B T 5 10 1 - × wire B Exercise
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Prof. Yong Chen ( yongchen@purdue.edu ) Prof. Michael Manfra ( mmanfra@purdue.edu ) Lecture 10 Slide 5 PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http://www.physics.purdue.edu/academic_programs/courses/phys272/ Electron current vs. conventional current v nA i t v nA n t i = = = ) volume ( where n is the mobile electron density, A is the cross-sectional area of wire, is the average drift speed of electrons, and in a metal. v
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Lecture13_2011 - PHYS 272: Matter and Interactions II -...

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