问题 探究题

请同学们观察下列实验:    

演示实验  取两个相同的验电器A和B,使A带电,B不带电.再用金属棒把A和B连接起来,观察验电器金属箔的角度有什么变化?  

(1)实验现象:________________________________.这说明,有_______通过金属杆从验电器A流动到B,使验电器B也带了电.也就是说金属杆上有了电荷的_______移动.    

教师进一步引申总结:    

(2)我们把善于导电的物体叫_______;把不于导电的物体叫___________.常见的导体有:_________;常见的绝缘体有:___________.    

(3)金属是最重要的导体.在金属导体中,部分电子可以脱离开原子核的束缚而在金属内部自由移动,这种电子叫做__________.金属导电,靠的就是__________.

答案

(1)A的金属箔张开的角度减小B的金属箔张开;电荷;  定向  

(2)导体;  绝缘体;  人体、大地、石墨、各种金属和酸碱盐溶液;   干木、陶瓷、玻璃、橡胶、油、塑料  

(3)自由电子  ;自由电子

阅读理解

阅读理解。

     To wash yourself, you take a bath (洗澡) or a shower. Animals need to keep clean, too. How do animals

clean themselves?

     Cats lick (舔) themselves to keep their fur clean. Have you ever watched a pet cat clean itself? Elephants

take baths much as you do. But instead of jumping into the tub (浴缸), they walk into a river or lake.

     Pigs also like to roll around in water. This keeps them clean and cool. If there is no clean water, they will

roll in mud (泥) on a hot day. They do this to cool off. Pigs do not really like mud. They are happier in a nice,

clean pond (水池).

     Bats have a funny way to keep clean. They lick their thumbs to clean their ears!

     Guess how polar bears clean themselves. They use snow, of course!

     Some animals take baths in dust instead of water! The wombat (毛鼻袋熊) is an Australian animal with

lots of fur. To get clean, it lies down. Then it covers itself with sand! Birds clean themselves in many ways.

Sometimes they wash in water. That's why some people put birdbaths in their yard. At other times birds take

dust baths, just like wombats.

     Birds also use their beaks (喙) to keep their feathers clean. They use their beaks the way you use a comb.

     Sometimes a bird has itchy bugs (发痒的虫子) in its feathers. Birds may use ants to help them clean off

the bugs. A bird will lie down on an ant nest. Then the ants will crawl on the bird. The ants make a kind of

bug spray (喷雾) on the feathers;. Then the itchy bugs die!

     Birds take baths in something else besides dust and ants! Some birds take "smoke baths" They sit on

chimneys. They wave their wings in the smoke!

1. This passage mainly tells us _____. [ ]

A. why some people put birdbaths in their yard

B. why birds allow ants to crawl on their body

C. how animals cool off on hot days

D. how some animals keep clean

2. What is a pig's favorite way to get clean? [ ]

A. Licking itself.

B. Lying down on ants.

C. Rolling in nice, thick mud.

D. Taking a bath in clean water.

3. Which of the following animals use dust to clean themselves? [ ]

A. Cats.

B. Bats.

C. Wombats.

D. Ants.

判断题