问题 单项选择题

有一容量为10kVA的单相变压器,电压为3300/220V,变压器在额定状态下运行。在理想的情况下副边可接40W,220V,功率因数cos=0.44的日光灯()盏。

A.110

B.200

C.250

D.125

答案

参考答案:A

解析:

变压器的额定功率用视在功率表示,它等于变压器初级绕阻或次级绕阻中电压额定值与电流额定值的乘积。值得注意的是次级绕阻电压是变压器空载时的电压,可以认为变压器初级端的功率因数与次级端的功率因数相同

阅读理解

阅读理解

       Do you know how to be a healthy kidll Here are some rules you should follow.

       First, eat different food, especially fruit and vegetables. You may have a favorite, but you'd better

eat something different. If you eat different food, you'Il probably get more nutrients your body needs.

      Second, drink water and milk as often as possible. When you're really thirsty, cold water is the

No. 1 choice.  Milk is a great drink  that can give you more calcium(钙)that your body needs to grow

strong bones.

      Third, listen to your body. How do you feel when you are full? When you are eating, notice how

your body feels and when your stom- ach feels comfortably full. Eating too much will not make you

feel comfortable and will make you fat.

      Fourth, limit screen time. Screen time is the time you watch TV, DVDs and videos, or using

computers. It is good to take more exercise such as basketball, bike riding and swimming. You can't

watch TV for more than two hours a day.

      Fifth, be active. One thing you'd like to do, as a kid,js tofind out which activity you like best. Find

ways to be active every day. Follow these rules and you can be a healthy kid.

1. You should eat different food especially____     .

A. meat                  

B. hamburgers

C. sweets                  

D. fruit and vegetables

2. Which kind of drinks can give you more calcium?

A. Juice.                  

B. Milk.

C. Cold water.            

D. Tea.

3. According to the passage, you should follow_______rules if you want to be healthy.

A. five    

B. nine  

C. fifteen    

D. thirt.een

4. You should watch TV____      a day.

A. more than two hour        

B. less than two hours

C. more than three ho        

D. five hours

5. According to the passage, which of the following isTRUE?

A. When you're eating, you don't have to notice how your body feels.

B. You can eat your favorite food as much as possible.

C. You can watch TV as long as you like to get more information.

D. We should try to live in an active way in our life.

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