题目

如图所示，已充电的平行板电容器，带正电的极板接地，两极板间于P点处固定一负的点电荷，若将上极板下移至虚线位置，则下列说法中正确的是（ ）A.两极间的电压和板间场强都变小B.两极间的电压变小，但场强不变C.P点的电势升高，点电荷的电势能增大D.P点的电势不变，点电荷的电势能也不变 答案：【答案】BD【解析】试题分析：电容器与电源断开，所带电荷量不变，由场强公式和电容公式可知，由此可知场强正比于单位面积上的带电量，A错；B对；设正极板为Ｏ点，则，由此可知P点电势不变，点电荷的电势能也不变，D对；C错；任务型阅读。Dear Linda,     Thanks for your letter. I'm glad to hear you can come on Sunday. When you drive over to my house, it's easy to find the station. It's a little difficult after that. So here are some instructions(说明): Drive past the station. Don't turn left into Garden Road. Just go along New Street. There's a football ground on your left. Go straight ahead, past the bank, and turn left into Green Road. Turn left again into High Street. River Street is the first on the right. My house is on the right, across from a school.     See you on Sunday!                                                                                                                                                       Love,                                                                                                                                                          AnnA) 阅读这封信，在下面的地图上找出从火车站到Ann家的路线。并将表示她的寓所、足球场、银行和学校的序号写在横线上。     1. 在图中标出行走路线，用箭头指向Ann的寓所。2. Ann's house: __________3. Football ground: __________4. Bank: __________5. School: __________B) 根据信的内容，回答下列问题。6. Who's the letter from?__________________________________________________________________7. When will Linda visit Ann?__________________________________________________________________8. Who doesn't live in River Street, Ann or Linda?__________________________________________________________________9. Is it easy or difficult to find the station?__________________________________________________________________10. How will Linda get to Ann's house?__________________________________________________________________