Lecture 18

Lecture 18 - Quiz Quiz 3 + =...

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uiz 3 Quiz 3 • <Problems>+<Multiple Choice> = <34>+<34>. • Bring grading issues to your primary studio instructor within one week of receipt.

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Faraday’s Law of Induction •If we: ove a coil towards or away from a coil or – Move a coil towards or away from a coil, or – Move a coil towards or away from a magnet, or otate a coil about a magnet, or Rotate a coil about a magnet, or – Rotate a magnet across a coil, then •A current flows in the coil, implying that a voltage difference develops around the coil. •The summary of this is Faraday’s Law: the voltage ifference around a closed loop equals the negative rate of difference around a closed loop equals the negative rate of change of magnetic flux through the loop. Φ = = Δ dt B d d E V l
lux reminder Flux reminder • The flux of B through a surface is Φ = B •d A over the B surface, where dA=da n is a little piece of surface area da with the unit vector n pointing at right angles to the surface. • If B is constant and the surface is flat then Φ B =BAcos θ , where θ is the angle between B and n ; but B does not ave to be constant have to be constant. • In Faraday’s law, the flux is computed through an open surface, not a closed surface as is the case for Gauss’s aw for the E eld Law for the E-field. • There is a use for the magnetic flux through a closed surface, and it is

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auss’s Law for Magnetism Gauss s Law for Magnetism •The flux of B through an closed urface is zero or surface is zero, or r r •Gauss’s Law for B is important for 0 A d B what it says about possible types of B- fields. The simplest is the dipole. No magnetic monopoles are possible. By contrast, electric monopole (point charge) and dipole fields both exist. ut it is rarely useful for finding B •But it is rarely useful for finding B- fields.
test of the idea A test of the idea • Faraday’s Law predicts that flux change matters. The relative motion of the magnet and coil in the previous examples produces the flux change; but the motion itself

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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 18 - Quiz Quiz 3 + =...

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