题目

如图14-6-15所示，电压为10 V，R1=4 Ω，R2=6 Ω，电容器的电容C=30 μF. 图14-6-15(1)闭合开关S，电路稳定后，求通过R1的电流;(2)再断开开关S，求这以后流过R1的电荷量. 答案：解析：(1)S闭合，电路稳定后，即为R1与R2的串联电路，所以流过R1的电流为A=1 A，此时电容器与R2并联，两极间电压U2=IR2=6 V，且上板带正电荷.(2)断开S后，由于U=10 V，所以电源继续给电容器充电至极板间电压U2′=U=10 V为止，仍是上极板带正电，流过R1的电荷量等于继续给电容器的充电荷量，即ΔQ=C(U2′-U1)=30 (1) Which train(s) can people take at City Library? [　　] A．Only Red Train B．Yellow Train and Blue Train C．Only Blue Train D．Red Train and Blue Train (2) David want to go to Airport. He takes Yellow Train at High School.How many stations will the train stop at? [　　] A．2 B．4 C．5 D．11 (3) Sue takes the train at Zoo. Which station is NOT on her way to Old Garden? [　　] A．New Theatre B．Long Street C．City Bank D．Green Park (4) Bill lives near City Bank. He wants to go to High School. First, he takes Red Train. At which station should he change the train to Yellow Train? [　　] A．New Theatre B．Post Office C．Long Street D．Green Park (5) If a man wants to go from New Theatre to Post Office, the trains he should take are ________. [　　] A．Red Train→Yellow Train→Blue Train. B．Yellow Train→Red Train C．Red Train→Blue Train→Yellow Train D．Blue Train→Yellow Train