如图所示的电路中，电源电压为6V且保持不变，电阻R1的阻值为10Ω。闭合开关S，电流表A的示数为0.8A。求：通过R1的电流和电阻R2的阻值。
通过R1的电流为0.6A；电阻R2的阻值为30Ω
题目分析：由电路图可知，两电阻R1、R2并联，电流表测干路电流．因为并联电路各支路的电压相等且等于电源电压，所以U1=U2=U=6V，根据欧姆定律得，通过R1的电流
；又因为在并联电路中，干路电流等于各支路电流之和，所以通过R2的电流I2=I-I1=0.8A-0.6A=0.2A，根据欧姆定律变形公式得电阻R2的阻值
| 根据表格内容完成下列短文。 | ||||||||||||||||
| It's useful to know how much money we usually spend on different things. Then, if we also know how much money we will have, we can decide which things we should buy now and which things we can go without or wait for. Here is a student's weekly budget (预算) during the school year.
have them at all. If he wants to save (节省) on bus fares, he can 1______ to class. If he doesn't buy any candy, he can save 2______ a week. Or he can save 3______ if he has no soft drinks. He can save on lunches if he brings his own. He may be able to save on VDs by borrowing them from his friends or 4______ second-hand (二手). He doesn't have to 5______ to the movies or restaurants. |