一电子仅受电场力作用，从高电势处移动到低电势处，则
A．电场力对电子做正功
B．电子的电势能减少
C．电子的动能减少
D．电子的动能和电势能的总和保持不变
CD
本题考查电场力做功与能量的关系，从高电势处移动到低电势处，电场力做负功电势能增加，只有电场力作用，则电子原来有一定的动能，后来一部分动能消耗了，电子的动能减少，电子的动能和电势能的总和保持不变即能量守恒；
口语应用。(每小题1分，共5分) 阅读下面对话，从方框内7个选项中选择5个恰当的句子完成此对话。
B: 1 Could you tell me the time of the last train to Beijing this evening? A: There’s one at 8:30. But I’m afraid all the tickets have been sold out. B: 2 A: The first train leaves at 9:15. B: 3 A: It arrives at 12:30. But may be a little late because of the bad weather. B: OK! 4 A: 418 yuan and half of it for a child below 12. B: 5 I’d like two tickets and another one for a child at the age of ten. Here is the money. A: Thank you! |