试题与答案

理想变压器原线圈接在如图所示的电压上,原副线圈匝数之比为10:1,串在原线圈上的

题型:多选题

题目:

理想变压器原线圈接在如图所示的电压上,原副线圈匝数之比为10:1,串在原线圈上的电流表的示数为1A,则以下叙述正确的是(  )

A.变压器输出功率为200W

B.若n1=100匝,则输出端线圈的磁通量变化率的最大值为2Wb/s

C.副线圈两端的电压表示数20V

D.变压器的输入功率是由发电厂的输出功率决定的

答案:

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One possible version:Dear Alice I’m worried about the situation you are facing , in which you find it difficult to get rid of the habit of reading novels. As we all...

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题型:选择题

实验室有一个旧的学生直流电源。输出端的符号模糊不清,无法分辨正负极。小明设计了下面的判断电源两极的办法。在桌面上放一个小磁针,在磁针东面放一个螺线管,如图所示。闭合开关,磁针指南的一端向东偏转。下列判断正确的是

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题型:阅读理解

Sometimes there doesn’t seem to be enough rain. Other times there is too much. Maybe thereisn’t a lot we can do to control the rain, but there is a lot we can do to reduce problems caused bydifferent rainfall patterns.

A new development at the London Wetland Centre in Barnes solves the problems of managingwater with a “Rain Garden”. We are likely to be hearing about it a lot more often over the next fewyears. The idea is that the garden owner can store rainwater and use it in dry periods. They canreduce the problems caused by extra rain this way.

One of the key problems that the rain garden tries to deal with is the problem caused by toomuch water in the street. In a natural environment, a lot of rainwater is sent back into the air byplants. Much is also absorbed deep into the ground, and flows into streams and rivers. What happensin city environments can be completely different —— a large amount of rainwater flows straight offthe hard surfaces of roofs and roads. The harder the rain, the less likely it will be absorbed into theground —— floods are the result. Rainwater running off roads is often polluted.

The rain garden deals with living plants rather than hard surfaces. Plants are designed to holdwater and release it slowly, either into the ground, to be absorbed by plant roots (and so eventuallyback up into the atmosphere) or to go down into the water table. Not only does the rain gardenreduce the amount of water that flows onto the street, but it helps to clean it because plants are very goodat breaking down pollutants(污染物).

小题1:What’s the main idea of the first paragraph?

A.Explaining why there is a lack of rain at times.

B.Introducing several different patterns of rainfall.

C.Telling us how to avoid problems caused by rain.

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A.harm the environment in the short run

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C.be turned down by most new developments

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A.floods are often the results of small rains

B.a heavy rain is less difficult for plants to absorb

C.the rain garden helps send rainwater back into the air

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A.The plants

B.The ground.

C.The water.

D.The street.

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