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Chapter 30 Serway & Beichner

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Force between two current carrying wires

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Electric current The Ampere The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 m apart in vacuum, would produce a force between them equal to 2 × 10 -7 Newton per meter of length.

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Fig 30-8, p.932

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Fig 30-9c, p.933

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Fig 30-1, p.927

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Fig 30-3, p.929 See Ex. 30.1

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Fig 30-7, p.931 See Ex. 30.3 @ z = 0z >> R

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Ch. 3010

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Fig 30-7b, p.931

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Fig 30-17, p.938

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Fig 30-12, p.935 for r > R for r < R Application of Ampère’s Law

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Fig 30-13, p.936

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Fig 30-19, p.939 Field inside Solenoid

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start 9/13/04

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Fig P30-20, p.940 Magnetic Flux B = BdA = BAcos

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Ampère’s Law One More Time Ampere’s law states that the line integral of B. ds around any closed loop equals o I where I is the total steady current passing through any surface bounded by the closed loop.

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Apply Ampere’s Law to red loop for a wire with a constant current I Now introduce a capacitor to interrupt the the circuit. What’s wrong? Use a power supply that will keep current constant as the cap is charged: +Q/-Q on left/right plate. Now Apply Ampere’s Law again.

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Now introduce a capacitor to interrupt the the circuit. If our power supply is strong enough to keep I constant, the gray surface will give B = 0! What’s wrong? Assume that I is constant. Apply Ampère’s Law to either the, white or gray surfaces, both of which are bounded by the red loop. This leads to:

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If the power supply can keep the current constant, the cap. will be charged: +Q/-Q on left/right plate. This establishes an E-field between the two plates. E = EdA = Q/ o Electric flux will change in time corresponding to an effective current called the Displacement Current

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Consider to different surfaces

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Fig 30-27, p.945 Orbital Motion of the Electron in an Atom

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Fig 30-28, p.946 Magnetic Moments due to Spin of electron, neutron and proton

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Table 30-1, p.946 ElectronProtonneutron -9281.41-0.966 Magnetic Moments 10 -26 J/T

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Polarization Generated Field points in the opposite direction

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Table 30-2, p.948

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Paramagnetism Generated field adds to applied field Atomic currents

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Diamagnetism Generated field opposes applied field

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Magnetic Domains

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The Earth as a big magnet

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l =0.4 m i = 10 A

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Fig P30-6, p.957

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Ch. 3037

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Ch. 3038

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Ch. 3039

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Ch. 3040

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