课程名称︰材料科学导论二 课程性质︰必带 课程教师︰郭博成教授 开课学院：工学院 开课系所︰材料系 考试日期（年月日）︰99/06/22 考试时限（分钟）：14:30~16:30 是否需发放奖励金：yes （如未明确表示，则不予发放） 试题 : (All of them are old questions...) 1.(a)Explain the origins of the magnetic moment of an atom. (b)Do all electrons have a net magnetic moment? Why or why not? (c)Do all atoms have a net magnetic moment? Why or why not? (15%) 2.Briefly describe the differences among diamagnetism, paramagnetism, ferromagnetism, antiferromagnetism, and ferrimagnetism. (20%) 3.Illustrate the boundart in T-H-J (temperature-magnetic field-current density) space seperating superconducting states and normal states. (20%) 4.Explain why the resistivity of metal is increased with temperature but the resistivity of intrinsic semiconductor is decreased with increasing temperature. (15%) 5.How does the electron structure of an isolated atom differ from that of a solid material? (10%) 6.Some hypothetical metal is known to have an electric resistivity of 4x10^8 (ohm-m). Through a specimen of this metal that is 25mm thick is passed a current of 30A; when a magnetic field of 0.75 tesla is simultaneously imposed in a direction perpendicular to that of the current, a Hall voltage of -1.26x10^-7 V is measured. (a) Compute the electron mobility for this metal,and (b) the number of free electrons per cubic meter. (20%) --

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