山东建筑大学电工学期末考试试卷.doc

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1、山东建筑大学试卷共4页第1页BARP－12V+12V得分阅卷人一、填空。（每空1分，共20分）1．图示电路中，当将电位器RP的滑动触点向下滑动时，A点的电位，B点的电位。（填增高或降低或不变）2．已知正弦交流电压的有效值为220V，频率为50Hz，初相角为－45º，则其瞬时值表达式为。3．在RL充电电路中，时间常数τ=，τ越小，充电时间越。4.在RLC串联电路中，下列各式正确的有，。（填序号）①U=UR+UL+UC；②Z=R+j(XL+XC)；③；④P=RI25．一般来说，交流电路中的负载常为性负载，因此通常用于提高功

2、率因数的方法是_________，此时电路中的有功功率。6．三相对称电动势的特点是、、。7．负载三角形连接的三相对称电路，从大小上看，线电流为相电流的倍，从相位上看，线电流（填超前或滞后）相电流°。8．在三相交流电路中，各相有功功率分别为P1、P2、P3，无功功率分别为Q1、Q2、Q3，视在功率分别为S1、S2、S3，则总有功功率为P=，总无功功率为Q=，总视在功率为S=。9.铁心线圈中，铁心是由彼此绝缘的硅钢片叠成，这样做是为了减小。得分阅卷人二、（10分）已知：E1=15V，E2=10V，R1=0.5Ω，R2=1Ω

3、，R3=3Ω。试用支路电流法求各支路电流I1、I2和I3，并说明E1、E2分别起电源作用还是负载作用。班级姓名学号山东建筑大学试卷共4页第2页得分阅卷人三、（10分）如图所示电路，t=0时开关闭合，设换路前电路已处于稳定，R1=2kΩ，R2=3kΩ，C=250μF。要求：CuC--25V+R1R2+（1）求出开关闭合后的电压uC。（2）画出uC的变换曲线。···················································································

4、························装订线··································································································得分阅卷人四、（10分）已知：由R=30Ω，L=31.85mH，C=79.6μF组成R、L、C串联电路，接到220V、50Hz的交流电源上。试求：（1）感抗XL，容抗XC和总阻抗Z。（2）电路中电流i的有效值。（3）若通过调节电源频率使电路中发生谐振，则电源频率应为多少？i

5、+uC-+uL-+uR--+RLCu山东建筑大学试卷共4页第3页···········································································································装订线··································································································得分阅卷人五、（10分）5A20V4W6WI

6、+-4W4W电路如下图所示，试用戴维宁定理求电流I。得分阅卷人六、（10分）把电阻R=8Ω的扬声器接于输出变压器的二次侧，设输出变压器的一次侧绕组为500匝，二次侧绕组为100匝。试求：（1）折算到变压器一次侧扬声器的等效阻抗；（2）在变压器的一次侧接入电动势有效值为10V，内阻R0=200Ω的交流信号源时输送到扬声器的功率；（3）直接把扬声器接到上述交流信号源时输送到扬声器的功率。·····································································

7、······································装订线··································································································山东建筑大学试卷共4页第4页···········································································································装订

8、线··································································································得分阅卷人七、（20分）三相异步电动机的额定数据如下：f=50Hz，PN=4kW，nN=1440r/min，UN=220/380V，△