问题 填空题

某同学要测一个额定电流为0.3A的小灯泡的额定功率,他设计了如图所示电路图,请帮助该同学完成下列问题:

(1)在连接实物电路过程中,开关应处于

       状态。

(2)经检查电路连接无误后,接通电路,观二察到电流表指针位置如图所示,此时电路中电流为     A。

(3)假设实验时电路连接正确,器材及各接线柱的连接完好,实验中无论怎样调节滑动变阻器的滑片,电路中的电流总低于0.3A,其原因是                          

答案

(1)断开(2)0.13)电源的电压过低

考查知识点:电功率的测量.

思路分析:(1)为了保护电路,连接电路时开关要断开;

(2)首先确定使用的量程,然后确定每一个大格和每一个小格代表的示数,读出电流的大小;

(3)实验时电路连接正确,器材及各接线柱的连接完好,只能是电源电压过低,使电路中的电流达不到0.3A.

具体解答过程:(1)在连接实物图时,为了保护电路,开关要处于断开状态;

(2)从图中可以看出电流表的量程为0.6A,分度值为0.02A,因此电流值为0.1A;

(3)因为实验时电路连接正确,器材及各接线柱的连接完好,所以原因只能是电源电压太低.

故答案为:(1)断开;(2)0.1;(3)电源电压小于灯泡的额定电压.

试题点评:本题考查实物连接的注意事项、电流表的读数及故障分析等;为了安全,连接电路时,开关应断开,滑动变阻器接入电路的阻值应为最大.

单项选择题
阅读理解

You’re lost in the world of dreams and sleep. You roll over, smiling as you come across a swimming pool filled with chocolate. And then, your wonderful dream becomes a nightmare when someone is screaming, “Get up!” It’s just what every teenager goes through each morning!

Now, there seems to be one school that finally understands that requiring teens to show up at 9 am is not just cruel but also harmful to both the kids and the school.

The Monkseaton High School in North Tyneside, Britain, recently decided to experiment to see if there is any difference in student behavior if they just pushed back the start of their day by one hour, from 9 am to 10 am. And the results are surprising.

Since carrying out the later start, Monkseaton has seen a 28% drop in truancy, even hardly any lateness, and best of all, higher test scores. One of the reasons is that the teenagers are much happier to have the extra hour of sleep, but there is also a scientific reason behind why they need the extra sleep.

The school’s decision to push back the time was based on the research done by Oxford Professor Russell Foster, who pointed out that teenagers and adults have different sleep cycles, explaining why teenagers go to bed late and wake up late.

While adults are wide awake and ready at 8 am, teenagers are not fully awake until 10 am, sometimes even noon. Teachers may argue that their students perform better in the morning, but in fact, it is because they are in the zone while their students are still sleepy, making the students easier to control. Memory tests prove that the more difficult classes should be in the afternoon when teenagers are most wide awake.

The Monkseaton school officials are encouraged by the results and plan on voting to make it a permanent change.

小题1:What’s the best title of this passage?

A.Get up early, teenagers!

B.Finally, a school understands teenagers.

C.Why do teenagers stay up late?

D.Difference between teens and adults.小题2:What’s the meaning of the underlined word “truancy”?

A.grades

B.subject s

C.absence

D.classes小题3:What can we learn from the passage?

A.Teenagers and adults have the same sleep cycle.

B.Teenagers are fully awake at 10 am.

C.Teenagers are much happier to sleep than study.

D.Teenagers need the extra sleep also for a scientific reason.小题4:Which of the following statements is NOT true according to the passage?

A.The Monkseaton school is satisfied with the result of experiments.

B.It is cruel for the teenagers to show up at 9 am.

C.The Monkseaton school plans to change the school time forever.

D.Teenagers perform better in the morning than in the afternoon.