问题 实验题

王强同学观察到现在的手电筒大都由原来的一个小灯泡换成了多颗发光二极管,他通过使用发现这种手电筒非常明亮而且还非常省电。他很好奇,于是就到电子器材商店买了两颗这种发光二极管准备用实验测出它的额定功率。从包装盒上,他了解到这种发光二极管的额定电压是3V,正常发光时电阻约为80Ω左右。当他选好器材(电源是电压为6V的蓄电池,滑动变阻器上标有“20Ω 1A”字样)并将实验电路连成如图甲所示的情况后: 

 

(1)请你用笔画线当导线,替他把电路连接完整(要求选择合适的量程,导线不交叉);

(2)实验前,老师建议王强同学先使用电压表的大量程。王强将电路连好并检查无误后,应将滑动变阻器滑片移到     端(选题“A”或“B”)。这时,他闭合开关后发现发光二极管非常明亮且还冒烟,接着就被烧坏了。产生这种现象的原因是                  

(3)当王强找到原因换上合适的器材后,按照正确的操作规则将电压表的示数调到 3 V,这时他观察到电流表示数如图乙所示.则这时通过发光二极管的电流是        A,发光二极管的额定功率是        W;

(4)在这个实验中,滑动变阻器所起的作用是:

①                             ;②                              

答案

B,滑变阻值太小,0.04,0.12,保护电路,改变二极管两端电压

题目分析:(1)发光二极管的额定电压为3V,所以电压表的量程为0~3V,且与发光二极管并联;发光二极管的额定电流约为,故电流表的量程为0~0.6A,且与发光二极管串联,如图所示:

(2)由图可知,滑动变阻器滑片位于A端时接入电路的电阻最大;发光二极管被烧坏了说明电路中的电流过大,即滑动变阻器的最大阻值太小造成的.

(3)按照正确的操作规则将电压表的示数调到3V;电流表的量程为0~0.6A,分度值为0.02A,所以电流表的示数为0.04A,发光二极管的额定功率

(4)滑动变阻器的作用是:①保护电路;②调节发光二极管两端电压.

点评:本题考查了连接实物图、滑动变阻器的作用、电流表读数、求发光二极管的功率等内容,是实验的常考内容.

写作题

写作。

阅读下面的短文,然后按照要求写一篇150词左右的英语短文。

     There have been many types of ecological disasters caused to the Australian ecosystem by

introducing other animals. The most famous one was the introduction of the rabbit. The rabbits

in Australia are mostly from a group of wild rabbits in south eastern Australia. These were released

in the hope of starting a business selling rabbits’ skin. This did actually happen, but there was nothing

to stop the rabbits spreading to the rest of mainland Australia. Now we have billions. They compete

with the native animals, damage the vegetation and severely reduce the potential carrying capacity of

the land for grass-eating animals like sheep and cattle.

    As well as the disasters caused to the land ecosystem, there have been ones in the water. The most

obvious one was the deliberate introduction of European carp (欧洲鲤鱼) to the River Murray. The

carp were introduced to eat the weeds growing in the river. Now they have taken over much of the

river’s ecosystem and severely reduced the number of native fish.

Not all destructive introductions in Australia were of foreign species. There are several cases of native

Australian animals being taken to different places in Australia and causing destruction. Koalas were

introduced to Kangaroo Island and increased to such an extent that they are killing off the Manna Gum

trees.

【写作内容】

1. 以约30词概括阅读材料的主要内容;

2. 由于人类无休止地向大自然索取,无限制的掠夺自然,造成了资源枯竭等。大自然

毫不留情地对人类进行了报复。请你以约120个词谈谈你对人类和大自然和谐相处的看

法,内容包括:

(1) 你认为人类为什么要与大自然和谐相处?

(2) 举例说明人类与大自然由于不和谐相处而带来的灾害。

(3) 在日常生活中,我们应该怎样与大自然和谐相处。

【写作要求】

1. 在作文中可以使用自己亲身的经历或虚构的故事,也可以参照阅读材料的内容但不

得直接引用原文中的句子;

2. 作文中不能出现真实姓名和学校名称。

【评分标准】

概括准确,语言规范,内容合适,篇章连贯。一些科学事实。

__________________________________________________________________________

__________________________________________________________________________

单项选择题