课程名称︰电磁学(上) 课程性质︰系必修 课程教师︰陈政维 开课学院：理学院 开课系所︰物理学系 考试日期（年月日）︰2009/01/12 考试时限（分钟）：125 是否需发放奖励金：是！ 试题 : 1.(a) A dipole ｐ is a distance r from a point charge q, and oriented so that ｐ makes an angle θ with the vector r from q to ｐ. What is the force on ｐ? (b) A point charge q is situated a large distance r from a neutral atom of polarizability α. Find the force of attraction between them. 2.(a) Suppose the entire region below the plane z = 0 is filled with uniform linear dielectric material of susceptibility χe. Calculate the force on a point charge q situated a distance d above the origin. (b) A point charge q is imbedded at the center of a sphere of linear dielectric material (with susceptibility χe and radius R). Find the electric field, the polarization, the bound charge densities ρb and σb, and the total bound charge on the surface. 3.(a) Find the magnetic field a ditance z above the center of a square of widths a, which carries a steady current I. ︿ (b) An infinite uniform surface current Ｋ = Kｙ flows over the xy plane at z = 0. Please find the magnetic field Ｂ. 4.(a) Find the vector potential of an infinite solenoid with n turns per unit length, radius R, and current I. ︿ (b) A long circular cylinder of radius R carries a magnetization Ｍ= ks^2ψ, ︿ where k is a constant, s is the distance from the axis, and ψ is the azimuthal unit vector. Find the magnetic field due to Ｍ, for points inside and outside the cylinder. 5.(a) Starting from the Lorentz force law, Ｆmag = I∫(dｌ×Ｂ), show that the torque on any steady current distribution in a uniform field Ｂ is ｍ×Ｂ. (b) A current Iflows down a long straight wire of radius a. If the wire is made of linear material of susceptibility χm, and the current is distributed uniformly, what is the magnetic field a distance s from the axis? Also please find all the bound currents. 1 Note: ａ = ∫dａ = ／ ∮ｒ×dｌ. s 2 --

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