1一、(本题共18分,包含3个小题,每小题6分)1.单口网络如图1.1所示,试求端口短路电流SCI和等效电阻0R,并画出其诺顿等效电路。图1.1A5.466//326//33233//2618SCI426//30R画诺顿等效电路2.试将图1.2所示各单口网络等效变换为最简单的形式。3.电路如图1.3所示,求受控源所提供的功率。V3325UUUW362)9(UUP受控源提供W36功率。(b)(a)(c)+18V-6Ω1A2Ω2A(b)图1.2(a)+6V-5A2A6Ω(c)-18V++6V-6Ω3Ω+6V-9V+-6A8A图1.35A9V+-+U-2U3Ω+18V-6Ω2Ω6A3Ω2二、(本题共12分,包含2个小题,每小题6分)1.电路如图2.1所示,试用叠加原理求电压U。9A电流源起作用时:V189)6//3(U15A电流源起作用时:V0U18V电压源起作用时:V1218636UV6UUUU2.电路相量模型如图2.2所示,已知V6011U,求该单口网络的有功功率P、无功功率Q、视在功率S和功率因数。4525.55.5j5.55j//)6j7(2ZA1524525.56011ZUIW1145cos211cosUIPvar1145sin211sinUIQAV56.15211UIS707.045coscos三、(本题共12分,包含2个小题,每小题6分)1.正弦稳态电路如图3.1所示,已知Vcos210)(Sttu,5R,H20mL,F8C,且)(Stu与)(ti同相位。(1)求电压源)(Stu的角频率;求电流)(ti的有效值I;(3)求电压)(Ltu和)(Ctu的有效值LU和CU。sradLC/250010810201163A2510SRUIV1002102025003LILUV10021082500116CICU图2.2+-j5Ω2Ω-j6Ω7ΩUI图2.115A+U-18V+-8Ω3Ω9A6Ω5Ω10ΩLuL(t)+-i(t)+uC(t)-C+uS(t)-R图3.132.二阶电路如图3.2所示。(1)列写出以)(Ctu为变量的电路微分方程;(2)判断电路的阻尼性质(过阻尼,欠阻尼,临界阻尼)。18dd32.0dd16.0ddddCC2C2SCC2C2ututuUutuRCtuLC(4)1008.0224d0RR欠阻尼四、(本题共12分,包含2个小题,每小题6分)1.无源单口网络N0如图4.1所示,已知V3cos6cos1020)(tttu,A)603cos(25)(tti。(1)求单口网络N0所消耗的平均功率P;(2)求电压)(tu的有效值U;(3)求电流)(ti的有效值I。W10360cos2226520PV63.212621020222UA20.522522I+uC(t)-0.08F2H+18V-4Ω图3.2图4.1+u(t)-i(t)N042.电路如图4.2所示,已知V)752cos(22416)(Sttu,电路已处于稳态,求电流)(ti。V16)(Stu单独作用时:A2816)(tiV)752cos(224)(Sttu单独作用时:45288j83j//)6j(2j8ZA302345287524IA)302cos(3)(ttiA)302cos(32)()()(ttititi五、(本题共16分,包含2个小题,每小题8分)1.电路如图5.1所示,用网孔分析法求电流I。标注网孔电流和电压U612108)83(10106)62(2121IIUIUIA210V26A6A12121IIUII图4.2i(t)+uS(t)-1.5H8Ω1HF121+U-I1I210A图5.110A12V-+10V-+I6Ω8Ω2Ω6A3Ω52.电路如图5.2所示,用节点分析法求电压U。标注节点号和接地符号UUUUUUUU2112215.010110181210110121V2V6.5V6.721UUU六、(本题10分)电路如图6所示。(1)若负载k12LR,求LR获得的功率LP;(2)若负载LR可变,要使LR获得最大功率,LR应为何值?并求LR获得的最大功率LmaxP。V169103105.1105.1510210733333OCUk8103//105.11073330RmW68.710121012108163233L2L0OCLRRRUP当k80LRR时,mW810841643202OCLmaxRUP图6+9V-3kΩ+5V-7kΩRL2mA1.5kΩ21图5.2+U-2U10Ω0.5A2Ω8Ω6七、(本题10分)电路如图7所示,已知0t时开关K闭合,闭合前电路已处于稳态,(1)求电压)(Ctu,0t;(2)求电流)(ti,t0;(3)画出电压)(Ctu和电流)(ti的变化曲线。V36656)0(CuV12663335636)(Cus11.0)86//3(0CRVe2412e)()0()()(--CCCCttuuutu,0tAe4.2d)(d1.0)(-Ctttuti,0t两条曲线八、(本题10分)正弦稳态电路如图8所示,已知VSttu5cos12)(,求电流)(ti、)(1ti和)(2ti。画相量模型45233j36//)2j8j(6jZA)455cos(22)(A45245230212SttiZUIA5cos2)(A0266j611ttiIIA)905cos(2)(A90266j6j22ttiII图8i1(t)i2(t)i(t)0.4H+uS(t)-0.025F1.2H6Ωi(t)图7Kt=0+uC(t)-0.1F8Ω+6V-6Ω3Ω5A