问题 问答题 计算题

某低压客户报装容量为单相220V、2kW电动机2台和200W照明负荷,问该用户应配用多少安的电能表和至少多大截面的接户线?

答案

参考答案:

电动机负载电流I=2×2000÷220=18.2(A)

照明负载电流I=200÷220=0.9(A)

总负载电流I=18.2+0.9=19.1(A)

根据最大负载电流可知,应选配5(20)A或5(30)A的单相220V电能表和至少4m2铜芯或10m2铝芯接户线。

选择题
阅读理解

You cannot see any object unless light from that object gets into your eyes. Some of the things you see give off light of their own. The sun, the stars, a lighted lamp are examples that can be ssen by their own light. Such things are luminous. Most of the things you see are not giving off light of their own. They are simply reflecting light that falls on them from the sun or some other luminous bodies. Then moon , for example , does not give off any light of its own. It is non-luminous. You see it because sunlight falls on it and some of it reflects in your direction. So moonlight is only secondhand sunlight.

When you look at a book, it sends your eyes some of the light that falls on it, and you see the book. If light could be kept out from where you are so that there would be no light for the book to reflect, then you could not see the book even with your eyes wide open.

Light travels so fast that the time in which it travels from the book you are reading to your eyes is so short as if it took no time at all. Light reaches us form the moon , which is about 380,000 kilometers away, in only a little more than a second.

小题1:You can see the book because___________.

A.your eyes are close to it .

B.it reflects light

C.it has light of its own

D.your eyes can get to it小题2:The word “ reflects”  means____________.

A.throws back

B.takes back

C.gives off

D.sends out小题3:    ___________ have light of their won.

A.the sun and the moon

B.The stars and the earth

C.The sun and the stars

D.The moon and the earth