问题 填空题

将一电量为q=2×10-6C的点电荷从电场外一点移至电场中A点,电场力做功为4×10-5J,则A点的电势为______V,如果把q=-4×10-6C的电荷放在A,则电荷具有的电势能为______J.

答案

A与电场外一点的电势差为U外A=

W
q
=
4×10-5
2×10-6
V=20V.由题分析可知,电场外一点电势大于A点电势,电场外一点电势为零,则A点的电势为-20V.把q=-4×10-6C的电荷放在A具有的电势能Ep=qφ=-4×10-6×(-20)J=8×10-5J

故答案为:-20,8×10-5

阅读理解

Jenny lived in a town.Her father,Mr.Young,had a shop there and sold clothes in it.The shopkeeper was born in a poor family and was in school no more than a year.He was always sorry for it though he had much money now.He hoped his daughter could become a scientist.But the girl didn’t 1ike anything else except singing.She often went to the concerts,bought a lot of records the famous pop stars made and insisted on listening to the music when she was free.Of course she wanted to be a pop star,too.Her parents wanted to prevent her,but she didn’t listen to

them and they had to agree to her choice.They engaged an old man who was good at music as a private teacher.

Five years passed.Mr.Young bought all kinds of musical instruments for Jenny and they visited some places where the famous singers were born.Of course he spent a lot of money on it.But he found the girl didn’t make any progress.At last the teacher didn’t think the girl could become a singer at all and had to tell Mr.Young about it.The man became angry and said,“Why didn’t you tell me about it earlier? My daughter learned nothing but I paid you month after month!”

“I think you should thank me for it,”said the teacher.“Another teacher, who teaches

badly,is paid more than I was.And I saved much money for you!”

小题1:Mr. Young was in school for a short time because______  .

A.he was too poor to go on studying

B.he had to help his parents

C.he was weak in his lessons

D.he didn’t like studying at all小题2:Jenny spent much money buying records and went to the concerts in order to ______

A.visit some places

B.know some pop stars

C.become a pop star

D.1earn singing小题3:Mr.Young became angry because______.

A.he paid a lot of money to the teacher

B.his daughter decided to drop music

C.his daughter spent four years on music

D.the teacher taught his daughter nothing

选择题