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(31.13) (31.14) (31.15) Equation 31.12 is Gauss’s law: the total electric flux through any closed surface equals the net charge inside that surface divided by # 0 . This law relates an electric field to the charge distribution that creates it. Equation 31.13, which can be considered Gauss’s law in magnetism, states that the net magnetic flux through a closed surface is zero. That is, the number of Equation 31.14 is Faraday’s law of induction, which describes the creation of an electric field by a changing magnetic flux. This law states that the emf, which is the line integral of the electric field around any closed path, equals the rate of Equation 31.15, usually called the Ampère–Maxwell law, is the generalized form of Ampère’s law, and describes the creation of a magnetic field by an electric field and the line integral of the magnetic field around any closed path is the sum of $ 0 times the net current through that path and # 0 $ 0 times the rate of change of electric flux through any surface bounded by that path. Once the electric and magnetic fields are known at some point in space, the force acting on a particle of charge q can be calculated from the expression F " qE 2 qv " B (31.16) This relationship is called the Lorentz force law. (We saw this relationship earlier as Equation 29.16.) Maxwell’s equations, together with this force law, completely describe It is interesting to note the symmetry of Maxwell’s equations. Equations 31.12 and 31.13 are symmetric, apart from the absence of the term for magnetic monopoles in E and B around a closed path are related to the rate of change of magnetic flux and electric flux, respectively. Maxwell’s equations are of fundamental importance '
B&ds " / 0 I 2 1 0
/ 0
d! E dt '
E&ds " % d! B dt ' S
B&dA " 0 Summary 989 Faraday’s law of induction states that the emf induced in a circuit is directly (31.1) where ! B " &B & d A is the magnetic flux. $ " % d! B dt S U M M A R Y Take a practice test for this chapter by clicking on the Faraday’s law Ampère–Maxwell law The Lorentz force law Gauss’s law in magnetism |