搜题请搜索小程序“爱下问搜题”
问题 多选题

某学习小组设计了一种发电装置如图甲所示，图乙为其俯视图．将8块外形相同的磁铁交错放置组合成一个高h=0.5m、半径r=0.2m的圆柱体，其可绕固定轴OO'逆时针（俯视）转动，角速度ω=100rad/s．设圆柱外侧附近每个磁场区域的磁感应强度大小均为B=0.2T、方向都垂直于圆柱体侧表面．紧靠圆柱体外侧固定一根与其等高、电阻R1=0.5Ω的细金属杆ab，杆与轴OO'平行．图丙中阻值R=1.5Ω的电阻与理想电流表A串联后接在杆a、b两端．下列说法正确的是（　　）

A．电流表A的示数约为1.41A

B．杆ab产生的感应电动势的有效值E=2V

C．电阻R消耗的电功率为2W

D．在圆柱体转过一周的时间内，流过电流表A的总电荷量为零

答案

A、B导体切割磁感线产生的感应电动势为  E=Bhv

又  v=ωr

解得  E=2V

由于ab杆中产生的感应电动势E的大小保持不变，所以杆ab产生的感应电动势的有效值E=2V，则电流表A的示数为I=

E
R1+R
=
2
0.5+1.5
=1A．故A错误，B正确．

C电阻R消耗的电功率为P=I2R=12×1.5W=1.5W，故C错误．

D、由楞次定律判断可知，通过电流表的电流方向周期性变化，在一个周期内两种方向通过电流表的电量相等，所以在圆柱体转过一周的时间内，流过电流表A的总电荷量为零．

故D正确．

故选BD

阅读理解
阅读下面短文，根据上下文，从文后方框内选出适当的选项填人文中空白处，使短文内容完整正确，然后完成第5小题。
     Years ago, if a teenager (青少年) had some problems in her life, she might write in her diary. Now
a teenager with the same problems might go onto the Internet and write about them in a blog (博客).
In many ways, a dairy and a blog are almost the same. So, what makes a blog different from a diary?
     __1__ Usually, a teenager treats her diary like a book full of secrets. Both diaries and blogs tell what
happened to the writer that day.
     I have a little sister, and sometimes l go online to read her blog. She writes about things like waking
up early for swimming practice and not studying enough for her chemistry exam. __2__ Then, after
I finished writing, I would hide my diary in a secret place because I was worried that my sister might
read it!
     Because a blog is such a public way of writing, it has both good and bad points. __3__ If I am
angry with a friend during school and write something bad about her in my dairy, she will never know.
However, if my sister writes something bad about a friend, that friend may read her blog and get angry.
__4__
     A blog has good points, of course. People choose to write in blogs because they know that their
friends will read what they write. If I am feeling sad one day and write in my dairy, "No- body cares
about me", no one will know about it. However, if my sister writes the same words in her blog, her
best friends will quickly reply and tell her how much they like her.  Blogs help people stay in contact
(联系) with their friends and know what the people around them are doing.
If people are careful about what they write, blogs are a very good way to write about everyday life.
However, I still prefer my old diary!
A. So we have to be very careful of what we write.
B. When I was her age, I wrote about the same thing, but only in my diary.
C. The biggest problem with a blog is that anyone can read what you write.
D. The biggest difference is that a blog is much more public than a diary.
5. Which one is NOT the writer's idea?
A. A dairy is safer than a blog.
B. A dairy and a blog are almost the same in many ways.
C. Blogs can help people stay in contact with their friends.
D. Blogs are the best way to write about everyday life.
查看答案
单项选择题

对加工爆炸危险物品车间的厂房房顶描述正确的是（）。

A、为防爆，安装轻质房顶

B、为坚固，应采用重型房顶

C、以上都不对

D、为防爆，露天作业
查看答案