27 Magnetic Sources charge motion Gauss’s Law (again) Ampere’s Law materials
27-1 The Magnetic Field of Moving Point Charges
Current & Magnetic Field field circulation
(RHR) I B
field-effect ammeter
RHR Review Magnetic Force: cross-product rule (flat hand or “peanut butter jar”) Magnetic Field: thumb along I, B follows curled fingers
moving point charge B ~ qvsinq/r2.
27-2 The Magnetic Field of Currents: The Biot-Savart Law
Biot-Savart Law integrated field effect of current all dB same direction at center of hoop
B on axis of hoop dB not same direction non-axial component adds vectorially to 0 axial component remains
section-view of hoop-current axial B same direction is current in or out of screen at top of hoop?
electromagnet (solenoid)
solenoid high# turns/meter N = #turns, L = length (m) Bcenter = moNI/L n = N/L: Bcenter = monI
straight current-segment
Calculate B at Center in terms of L and I.
B of long straight current angles are + and – 90 degrees:
parallel wires same directed I’s attract, opposite directed currents repel.
Magnetic Force Balance Experiment
Magnetic Force Balance Experiment
the ampere current in two long parallel wires that causes a force of 2x10-7 newtons per meter of length of the wires.
27-3 Gauss’s Law for Magnetism
Gauss’s Law for B: Absence of Magnetic Charge Compare to Gauss’s Law for E: Qinside
E and B Fields: Similarities and Differences
27-4 Ampere’s Law
27-5 Magnetism in Matter
Magnetic Moments of an Un-magnetized Material
Magnetic Domains in Crystalline Silicone
Aligned Magnetic Domains Produces “Magnet”
Magnetic Field due to Naturally Occurring Magnetite
Magnetic “bits” Recorded on Magnetic Tape… 0, 1, 0 Cross Section of a Recording Head Solenoid
Magnetic Disk Hard Drive
Magnetic Disk Hard Drive: 2400x Magnification
Summary magnetic fields are due to charge motion biot-savart law determines B. B fields have no point source B integrated along a closed path is proportional to the current enclosed by the path magnetic materials
general biot-savart
two hoops