关于电势差和电场力做功的说法中，正确的是（ ）
A．电势差是矢量，电场力做的功是标量
B．在两点间移动电荷，电场力不做功，则两点间的电势差为零
C．在两点间被移动的电荷的电荷量越少，则两点间的电势差越大
D．在两点间移动电荷时，电场力做正功，则两点间的电势差大于零
A、电势差是标量，电场力做功也是标量．故A错误．
B、根据UAB=
知，在两点间移动电荷，电场力不做功，则两点间的电势差为零．故B正确．WAB q
C、两点间的电势差与移动的电荷无关，由电场决定．故C错误．
D、根据UAB=
知，电场力做正功，电势差不一定大于零，若电荷带负电，电势差小于零．故D错误．WAB q
故选B．
| 阅读下面的告示牌，选择最佳答案。 | |||
Ⅰ
| |||
| 1. From Sign I we know people _______ in the lake. | |||
| A. can swim B. cannot swim or fish C. can fish | |||
| 2. Where can we see Sign I in China? | |||
| A. On the Great Wall. B. By the West Lake. C. On Mount Emei. | |||
| 3. From SignⅡ,we know the cook (厨师) works _______ hours a week. | |||
| A. 20 B. 26 C. 28 | |||
| 4. From SignⅡ, we know that _______. | |||
| A. people can have breakfast at 5:45 on Monday B. People can have lunch in the restaurant on Saturday C. the restaurant is not open on Sunday | |||
| 5. If you read Sign Ⅲ, you will _______. | |||
| A. go along the road B. stop and stay there C. take another way |