Lecture 17

# Lecture 17 - Quiz Quiz 3 Is Friday March 26 4:30-5:45 CW101-102-103 Magnetic fields and forces Amperes Law Biot-Savart law magnets Review will be

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uiz 3 Quiz 3 • Is Friday, March 26, 4:30-5:45, CW101-102-103 • Magnetic fields and forces, Ampere’s Law, Biot-Savart law, magnets. • Review will be Wednesday evening, March 24, 7:30 PM, CW102. AS review will be Thursday arch 25 6:00PM asley SAS review will be Thursday, March 25, 6:00PM, Pasley Auditorium.

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agnets Magnets •We have spent quite a bit of time computing magnetic fields produced by current carrying wires. •But how does a “magnet” work? •The explanations starts with recognizing that electric currents operate at the microscopic level. e’ll try to show today the important connection between •We ll try to show today the important connection between angular momentum and magnetism. •And we’ll introduce the three most important types of magnetism: paramagnetism, diamagnetism, and ferromagnetism.
ipoles Dipoles • These are the key building blocks of natural magnets. • Along the axis, B a = μ 0 μ / 2 π ( R 2 +d 2 ) 3/2 Æ μ 0 μ / 2 π d 3 far from the dipole. • In the plane of the dipole (not derived here), B p Æ - μ 0 μ / 4 π d 3 . wo key points: Two key points: • The field strength is proportional to the dipole moment ( μ =current×area). • The field decreases in strength as 1/distance 3 .

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ipole fields, = Dipole fields, μ I A Coil 1 carries 1A of current in 1 loop around a 1 cm 2 area. Coil 2 carries 1A of current in 2 loops around a 2 cm 2 area. How large will coil 2’s field B 2 be compared coil 1’s field B t a distance of 1 m from the center of to coil 1s field B 1 at a distance of 1 m from the center of either coil? A. B /B =1/4. 2 1 B. B 2 /B 1 =1/2. C. B 2 /B 1 =1. D. B 2 /B 1 =2. E. B 2 /B 1 =4.
ore dipole fields: B /d 3 More dipole fields: B 1/d •S u ppose a small magnetic dipole produces a field B=8×10 -6 T in the plane of the dipole at a distance of 20 cm from the center of the dipole. What will be the field trength 40 cm from the dipole center in the plane of the strength 40 cm from the dipole center in the plane of the dipole? A. B=8×10 -6 T. B. B=4×10 -6 T. C. B=2×10 -6 T. D. B=1×10 -6 T.

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teracting coils Interacting coils uppose the coil at left carries current in the direction Suppose the coil at left carries current in the direction shown. A second coil to the right of the dashed line carries the same current. Which configuration of this econd coil will have the lowest potential energy (be in second coil will have the lowest potential energy (be in stable equilibrium)? A. Left-most. B. Middle. C. Right-most.
The Bohr model of the atom • This is a simple “planetary” model of an atom that works reasonably well for hydrogen. • We picture the electron as orbiting the nucleus (with charge Ze ) at a radius R . Newton’s laws then imply that F=kZe 2 /R 2 =mv 2 /R . Bohr’s part of the model was his bold assertion that the angular momentum L=mvR only took on integer multiples of the constant h/2 π , with h=6.6 × 10 -34 Js known as Planck’s constant; ie., L=n(h/2 ). ; , ( ) • The electron will pass a particular point once per revolution, implying a current I=e/T=ev/2 R ..

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## This note was uploaded on 05/11/2010 for the course ＰＨＹ 214 taught by Professor Timothybolton during the Spring '10 term at Kansas State University.

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Lecture 17 - Quiz Quiz 3 Is Friday March 26 4:30-5:45 CW101-102-103 Magnetic fields and forces Amperes Law Biot-Savart law magnets Review will be

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