问题 探究题

在探究“通过导体中的电流与电压、电阻的关系”的活动中,小明同学画出的电路图如图1所示.

(1)请将图2所示的实物连接成实验电路.

(2)连接电路时,开关应_________,变阻器的滑片P应置于_________端.(填“A”或“B”)

(3)小明接通电路后,发现电流表指针不偏转,电压表指针有明显的偏转,调节变阻器的滑片时也没有任何的变化.你认为电路中的故障是_________.

(4)排除故障后,小明首先研究导体中的电流与电压的关系,那么他应该控制_________保持不变;随后他又研究电流与电阻的关系,他控制电阻两端的电压为2V进行实验,第一次进行很顺利,第二次换上一个新的电阻后,无论怎样移动变阻器的滑片P,电压表的示数总是大于2V.出现这一现象的原因可能是(1条即可)_________.

答案

(1)

(2)断开;B;

(3)电阻R断路或电阻与接线柱接触不良;

(4)电阻;滑动变阻器阻值太小(或换上的电阻太大或电源电压 太大).

阅读理解

You may have seen a lot of frogs, but if you haven't, you must have heard about frogs. However, have you heard about a frog that can kill a person?

These small brightly colored amphibians (两栖动物) live in the tropical  rain forests of Central and South America. They are best known for their ability to kill persons even though they are no more than 2 inches long. If we touch their poisonous skin without proper protection (such as gloves), we may die! For animals of this size that can be so deadly, they are certainly one of the world's most poisonous animals! Who are they? They are poison arrow frogs or, simply, poison frogs.

Poison frogs acquired their name from the Indians. The Indians catch and kill many of these frogs before hanging them upside down over a campfire. As the frogs get hot, the poison drips out of their skin. The Indians collect the poisonous liquid in a bottle and dip(蘸) the tips of their arrows into the bottle. Once the tips are dried, they are ready to be used for their arrows for hunting.

There are about 170 different types of poison arrow frogs in the world. Though most species have bright markings, either in stripes or patches, on their black bodies, some just wear noticeable single-colored coats. Their shocking skin colors-usually in yellow, red, green, blue or orange-serve as a warning sign to other animals. The sign simply says,” Stay away or pay with your life!” They certainly do not bluff.

小题1:We can infer that the Indians may kill poison frogs in order to______.

A.treat diseases

B.avoid being bitten

C.hunt animals

D.eat their meat小题2:According to the passage,  poison frogs______.

A can grow to several meters long                   B. like to change colors on the back

C. have bright-colored skin or markings            D. are on the edge of dying out

小题3:Which of the following best explains the last sentence of the passage?

A.Poison frogs don't want to kill others.

B.Poison frogs do not just scare others.

C.Poison frogs want to stop others from coming near.

D.Poison frogs just pretend to be dangerous animals.

单项选择题