300 likes | 443 Views
Chapter 30. Serway & Beichner. Force between two current carrying wires. Electric current The A mpere
E N D
Chapter 30 Serway & Beichner
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.
See Ex. 30.1 Fig 30-3, p.929
@ z = 0 z >> R See Ex. 30.3 Fig 30-7, p.931
for r > R Application of Ampère’s Law for r < R Fig 30-12, p.935
Field inside Solenoid Fig 30-19, p.939
start 9/13/04
Magnetic Flux B = B•dA = BAcos Fig P30-20, p.940
Ampère’s Law One More Time Ampere’s law states that the line integral of B.ds around any closed loop equals moI where I is the total steady current passing through anysurface bounded by the closed loop.
Apply Ampère’s Law to either the, white or gray surfaces, both of which are bounded by the red loop. This leads to: Assume that I is constant. 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?
E = E•dA = Q/o Electric flux will change in time corresponding to an effective current called the Displacement Current If the power supply can keep the current constant, the cap. will be charged: +Q/-Q on left/right plate. This establishesan E-field between the two plates.
Orbital Motion of the Electron in an Atom Fig 30-27, p.945
Magnetic Moments due to Spin of electron, neutron and proton Fig 30-28, p.946
10-24 J/T Magnetic Moments 10-26 J/T Table 30-1, p.946
Polarization Generated Field points in the opposite direction
Paramagnetism Generated field adds to applied field Atomic currents
Diamagnetism Generated field opposes applied field