課程名稱︰普通物理 課程性質︰土木系必修 課程教師︰楊忠喜 開課學院：工學院 開課系所︰土木系 考試日期（年月日）︰2010/03/15 考試時限（分鐘）：120 是否需發放獎勵金：是 謝謝 （如未明確表示，則不予發放） 試題 : 1. Charge Q is on the y axis a distance A from the origin and charge q in on the x axis a distance d from the origin. Find the value of d in terms of A for which the x component of the force on q is the greatest. Ans: d=A/√2 2. A solid nonconducting sphere of radius R has a nonuniform charge distribution of volume charge density ρ=Ar , where A is a constant and r is the distance from the center of the sphere. The total charge on the sphere is Q. (a) E(R/2)=? Ans: Q/16πεR^2 (b) if V(∞)=0 find V(R/3) Ans: 107Q/324επR (c) find the total electrostatic potential energy V=? Ans: Q^2 /7πεR 3. 作圖:畫出電雙極之電力線和等電位面圖形 4. The dipole moment of a dipole is a 300 N/C electric field is initially perpendicular to the field, but it rotates so it is in the same direction as the field. If the moment has a magnitude of 2*10^-9 C*m , find the work done by the field Ans: 6×10^-7 J 5. What is the magnitude of the electric field at the point(3,-2,4)(m) if the eletric potential is given by V=6xyz^2 , where V is in volts. Ans: 450 V/n 6. Each of the four 25μF capacitors shown is initially uncharged. How many coulombs of charge pass through the ammeter A after the switch is closed? ＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿∥＿＿＿ ∣ ∣ ∣ ∣ ∣ ∣ ∣ = = 400V∣ ∣ ∣ ∣ ∣ ∣ ∣＿＿＿＿＿＿ A ＿＿＿＿＿＿＿＿＿ ∣＿＿∥＿＿＿∣ Ans: 0.133 C 7. An air-filled parallel-plate capacitor has a capacitance of 1pF. The plate separation is then doubled and a wax dielectric is inserted., completely filling the space between the plates. As a result, the capacitance becomes 2pF. Find the dielectric constant of the wax. Ans: κ= 4 --

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