问题 多选题

如图所示,电场中有A、B两点,则下列说法中正确的是(  )

A.电势ΦA>ΦB,场强EA>EB

B.电势ΦA>ΦB,场强EA<EB

C.将+q电荷从A点移动到B点电场力做正功

D.将-q电荷分别放在A、B两点时具有的电势能EPA>EPB

答案

电场线越密的地方电场强度越大,所以场强EA<EB

沿着电场线电势一定降低,所以电势∅A>∅B,故A错误,B正确.

C、将+q电荷从A点移动到B点所受电场力和电场线方向相同,电场力做正功,故C正确.

D、将-q电荷从A点移动到B点,所受电场力和电场线方向相反,电场力做负功,电势能增加,所以EPA<EPB,故D错误.

故选BC.

阅读理解

阅读理解。

                                                                  The Giraffe

      The giraffe is the tallest modem land animal. It can be over 5.5 metres tall. Its neck bone may be 1.9 metres

long. Yet the giraffe has only seven bones (骨) in its neck, the same number as in the human (人类). Even a

small bird has many more bones in its neck than in a tall giraffe. Each bone in a giraffe's neck is very long, while

the bones in a human neck are small. That makes the difference. A female (雌的) giraffe gives birth to one baby

at a time. The baby, called a calf, is about 1.9 metres tall at birth. By the age of eight it is full-grown. The giraffe

eats mostly leaves. Because it has a long neck, it can reach the leaves high up on the trees.

1. In this passage the underlined word "giraffe" means _______. [ ]

A. 鲸鱼

B. 长颈鹿

C. 大象

D. 恐龙

2. The number of the bones in a bird's neck is _______. [ ]

A. as big as in a human's neck

B. not so big as in a giraffe's neck

C. much more than in a human's neck

D. much smaller in a giraffe's neck

3. Which of the following is true according to this passage? [ ]

A. A giraffe has only seven bones.

B. Tile giraffe is the largest animal on land.

C. It takes eight years for a giraffe to grow up.

D. All the leaves on the trees will be eaten by giraffes if they live in that region.

4. The baby giraffe is about _______ at birth. [ ]

A. 5.5 metres long

B. 5.5 metres tall

C. 1.9 metres long

D. 1.9 metres tall

5. When a giraffe sees a tiger we can guess _______. [ ]

A. it will run away as fast as possible

B. it will run to eat the tiger

C. it will make the tiger bring it something to eat

D. it will bring some small animals for the tiger to eat

选择题