问题 选择题

图1、图2分别表示两种电压的波形,其中图1所示电压按正弦规律变化,下列说法正确的是(  )

A.图1表示交流电,图2表示直流电

B.两种电压的有效值相等

C.图1所示电压的瞬时值表达式位u=311sin100πtV

D.图1所示电压经匝数比为10:1的变压器变压后,频率变为原来的

1
10

答案

A、由于两图中表示的电流方向都随时间变化,因此都为交流电,故A错误;

B、由于对应相同时刻,图1电压比图2电压大,根据有效值的定义可知,图1有效值要比图2有效值大,故B错误;

C、从图1可知,Em=311V,ω=

T
=
10-2
=100πrad/s,所以图1电压的瞬时值表达式位u=311sin100πtV,故C正确;

D、交流电经过变压器后,频率不发生变化,因此D错误.

故选C.

阅读理解

John Denver has got international fame as a pop star, songwriter, actor and environmental activist ( 环境保护者). Songs like Take Me Home, Country Road, Rocky

Mountain High and Annie's Song have become very popular. But less than thirty years ago, John Denver was a young man with little more than a fine voice, a guitar, and a dream. Growing up in conservative (保守的) family, he was not believed to drop out of college and head to Los Angeles, where the music scene was flowering. Nor was he believed to succeed.

In Take Me Home, John Denver talked about the story that shaped his life, with the story of the rich inner journey of a shy Midwestern boy. With honesty and cleverness, he wrote about his childhood, the feeling of moving to Los Angeles as the 60s came, his first lucky breaks, his first songwriting success with leaving on a Jet Plane and finally got a world fame.

He also wrote about his relationship with his first and second wife, as well as his parents, his children, his partners through his life and his friends.

Honest and rich in the book that only a natural-born storyteller could write so well, Take Me Home is very good from the beginning to the end. It's like spending a few days with a good friend.

小题1:This passage is probably about         .

A.a book written by John Denver

B.the life and cause of John Denver

C.how to write pop songs

D.what Los Angeles was like小题2:Take Me Home is a name of       .

A.a famous book

B.a folk song in Los Angeles

C.a wonderful movie

D.a pop song by John Denver小题3: From this passage, we can conclude that       .

A.John Denver's family didn't want him to leave college

B.he often had trips when he was a shy boy

C.he moved to Los Angeles with his parents

D.his family believed he would succeed小题4: John Denver wrote his songs about many things except        .

A.his first success in songwriting

B.his family members including his parents, his wives and his children

C.the problems of environment

D.his life in los Angeles

单项选择题