问题 选择题

如图所示,一理想变压器原线圈匝数为n1=1000匝,副线圈匝数为n2=200匝,将原线圈接在u=220sin100πt(V)的交流电压上,副线圈上电阻R和理想交流电压表并联接入电路,现在A、B两点间接人不同的电子元件,则下列说法正确的是

A.在A、B两点间串联一只电阻R,穿过铁芯的磁通量的最大变化率为0.2 Wb/s

B.在A、B两点间接入理想二极管,电压表读数约为31V

C.在A、B两点间接人一只电容器,如果只缓慢提高交流电频率,电压表读数将缓慢增大

D.在A、B两点间接入一只电感线圈,如果只缓慢提高交流电频率,电阻R消耗电功率将缓慢增大

答案

BC

题目分析:在A、B两点间串联一只电阻R,输入电压最大值为220V≈311V,故平均每匝电压为0.311V,故磁通量的最大变化率为0.311Wb/s,A错误;输入电压有效值为220V,根据,故输出电压为44V;在A、B两点间接入理想二极管,会过滤掉负半周电流,设电压表读数为U,则根据有效值定义,有得:U=≈31V,B正确;在A、B两点间接入一只电容器,只提高交流电频率,电容器容抗减小,R分得的电压增加,电压表读数增加,C正确;在A、B两点间接入一只电感线圈,只提高交流电频率,感抗增加,R分得的电压减小,电压表读数减小,D错误。

阅读理解
Dear Parents,
As we start the second half of the spring term, I thought it important to update you on some key developments.
Post-16 Collaboration(合作)
We have entered into an exciting new collaboration with Bassaleg Comprehension School, Duffryn High School, St Joseph’s High School, and Coleg Gwent—The Newport West Post-16 partnership. We will be working together to deliver nearly 40 different courses at other schools and likewise, students from other schools will study some subjects here. Information about the courses available to students can be found on the partnership website www. Newftartwest. corn. uk.
Uniform
I would take this opportunity to remind all parents that students are not permitted to wear non-school uniform cardigans (开襟羊毛衫) in Newport High School. It is the responsibility of parents to make sure your son or daughter wears the correct uniform to school. This includes completely black shoes. Over the next half term we will be working with students to develop a cardigan with the school logo which will provide an alternative to the current school jacket.
School Catering.
We are currently seeking a new company to provide school meals. Our new catering provider will be in place at the start of the summer term and will be working with students, parents and staff to provide improvements to our current provision. I look forward to keeping you updated on this development.
Some key dates for you to be aware of over the next half term are:
Tuesday 15March
Year 9&10 Revision Conference
Wednesday 23 March
Year 12& 13 Parents Evening (4:00—7:00 p.m.)
Thursday 31st March
Academic Review Day
Friday 1st April
Teacher Training Day (school closed to students)
Friday 15st April
End of Spring Term
Tuesday 3rd May
Start of Summer Term
Thank you for your continued support.
Your faithfully,
Karyn Keane
小题1:Karyn Keane wrote the letter on behalf of ______.
A.Bassaleg Comprehensive SchoolB.Newport High School
C.St Joesph’s High SchoolD.Duffryn High School
小题2:What can be learned about the new collaboration?
A.It involves four schools altogether.
B.Course information will be mailed to every student.
C.Students can choose as many courses as they want.
D.It allows students to learn at other schools.
小题3:When will the new catering company start working?
A.In MayB.In April C.in MarchD.In June
小题4:What do we know from the passage?
A.Students will develop a logo for the school.
B.All parents will be invited to school on 23rd March
C.Students won’t go to school on 1st April.
D.The letter was written at the start of the spring term.
单项选择题 A1/A2型题