问题 选择题

一点电荷从静电场中的a点移动到b点,其电势能变化为零,则(  )

A.该点电荷一定沿等势面移动

B.a、b两点的电场强度一定相等

C.a、b两点的电势一定相等

D.作用于该点电荷的电场力总是与其运动方向垂直

答案

A、C点电荷从静电场中的a点移动到b点,其电势能变化为零,说明电场力做功为零,由电场力做功公式Wab=qUab分析得知,Uab=0,则a、b两点的电势一定相等,但该点电荷不一定沿等势面移动.故A错误,C正确.

B、a、b两点的电势相等,而电场强度与电势无关,所以a、b两点的电场强度不一定相等.故B错误.

D、电场力做功只与初末位置间的电势差有关,与运动路径无关,所以作用于该点电荷的电场力不一定总是与其运动方向垂直.故D错误.

故选C

阅读理解

阅读理解。

                                                    May: Happenings from the Past

     May 5,1884

     Isaac Murphy, son of a slave and perhaps the greatest horse rider in American history, rides Buchanan

to win his first Kentucky Derby. He becomes the first rider ever to win the race three times.

     May 9,1754

     Benjamin Franklin's Pennsylvania Gazette produces perhaps the first American political cartoon (漫画),

showing a snake cutsin pieces, with the words" Join or Dic" printed under the picture.

     May 11,1934

     The first great dust storm of the Great Plains Dust Bowl, the result of years of drought (干旱), blows

topsoil all the way to New York City and Washington, D.C.

     May 19,1994

     Jacqueline Lee Bouvier Kennedy Onassis, former first lady and one of the most famous people of the

1960s, died of cancer in New York City at the age of 64.

     May 24, 1844

     Samuel F.B Morse taps out the first message, "What Hath God wrought," over the experimental

long-distance telegraph line which runs from Washington, D,C, to Baltimore, Md.

1. We know from the text that Buchanan is _____.

A. Isaac's father

B. a winning horse

C. a slave taking care of horses

D. the first racing horse in Kentucky

2. What is the title of the first American political cartoon?

A. Join or Die

B. Pennsylvania Gazette

C. What Hath God Wrought

D. Kentucky Dorby

3. In which year did the former first lady Jacqueline die?

A. 1934

B. 1960

C. 1964

D. 1994

4. Which of the following places has to do with the first telegram in history?

A. Washington, D.C.

B. New York City.

C. Kentucky.

D. Pennsylvania.

单项选择题