lecture16

# lecture16 - Two questions: (1) How to find the force, F on...

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Two questions: (1) How to find the force, F on the electric charge, q excreted by the field E and/or B? (2) How fields E and/or B can be created? B v q E q F × + = 2 r Q k E = Gauss’s law for electric field Electric charges create electric field: For one not moving (v<<c) charge: Gauss’s law for magnetic field Magnetic charges do not exist: Amperes law Electric current creates magnetic field: (As we will see later, this law should be extended ) Maxwell’s equations 0 cos ε θ encl E Q A d E dA E = Φ 0 cos = Φ A d B dA B B encl I l d B dl B 0 cos μ = ; dt d B Φ - = Faraday’s law A changing magnetic field induces an EMF A changing magnetic flux induces an electric field ! - = A d B dt d l d E

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11. Electromagnetic induction (Faraday’s law) 1) Flux (review) Φ Φ A d B A d B d B B 2) EMF (review) l d E q l d F q dW ε 3) Faraday’s law dt d B Φ - = - = A d B dt d A changing magnetic flux induces an electric field! This electric field is not a potential field. The field lines form a closed loops. A changing magnetic flux induces an EMF Units: (weber) B ] = 1 Wb = 1 T · m 2 1 : loops For N N N = B Φ - EMF in the closed loop - flux through a closed loop - = A d B dt d l d E
The direction of any magnetic induction effect is such as to oppose the cause of the effect For instance: a current produced by an induced emf moves in a direction so that its magnetic field opposes the original change in flux N S v B N S v B S N v B S N v B I I I I Example: If a North pole moves toward the loop in the plane of the page, in what direction is the induced current? Since the magnet is moving parallel to the loop,

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## This note was uploaded on 02/11/2012 for the course PHYSICS 222 taught by Professor Ogilvie during the Fall '05 term at Iowa State.

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lecture16 - Two questions: (1) How to find the force, F on...

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