課程名稱︰普通物理學甲下 課程性質︰數學系必修 課程教師︰蔡政達 開課學院：理學院 開課系所︰物理系 考試日期（年月日）︰102/4/16 考試時限（分鐘）：110 是否需發放獎勵金：是 （如未明確表示，則不予發放） 試題 : General Physics Midtern Examination Date: April 16, 2013 Course no.:202 101A2, Course title:GENERAL PHYSICS(A)(2) 1. Three long wires are parallel to a z axis, and each carries a current of 10 A in the positive z direction. Their points of intersection with xy plane from an equilateral triangle with sides of 50 cm, as shown in Fig.A. Afourth wire (wire b) passes through the midpoint of the base of the triangle and is parrallel to the other three wires. If the net magnetic force on wire ais zero, what are the (a) size [10 points] and (b) direction (+z or -z) of the current in wire b[10 points] ⊙a ╱ ╲ 他真的是正三角形 ╱ ╲ y ╱ ╲ │ ⊙_____●_____⊙ └─x b Fig.A 2. In Fig.B,the ideeal battery has emf ε=30.0 V, and the resistances are R1=R2=14Ω, R3=R4=R5=6.0Ω, R6=2.0Ω,andR7=1.5Ω. What are the currents (a)i2 [4 points],(b)i4 [4 points],(c)i1 [4 points],(d)i3 [4 points],and (e)i5 [4 points]? i2 i4 ┌───┬───┬───┐ ΣR1 ΣR2 +│ ΣR7 Σ是電阻 ├───┤ ═↑ε ├───┐i5 i3ΣR3 ΣR4 -│i1 R5Σ R6Σ └───┴───┴───┴───┘ Fig.B 3. Fig.C shows across section of a long cylindrical conductor of radious a=4.00 cm containing a long cylindrical hole of radious b=1.50 cm. The central axes of the cylinder and hole are parallel and are distance d=2.00 cmapart; current i=1.50 Aisuniformly disttibuted over the tinted aria. (a) What is the magnitude of the magnetic field at the center of the hole?[10 points] (b) Discuss the two special cases b=0 and d=0 [10 points]. ◤ ◥ ◤ ◥ 大圓半徑 a 小圓半徑 b ◢█◣ 兩圓心相距 d ███ ◥█◤ ◣ ◢ ◣ ◢ Fig.C 4. Charge is uniformly distributed sround a ring of R=2.4 c, and the resulting electric field magnitude E is measures along the central axis (perpendicular to the plane of the ring). At what distance from the ring's crnter is E maximum?[20 points] 5. Two electrons are fixed 2.0 apart. Another electron is shot from infinity and stops midway between. What is its initial speed?[20 points] --

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