问题 问答题 论述题

二极管整流电路常采用电容滤波,晶闸管整流电路能否采用电容滤波?为什么?

答案

参考答案:

晶闸管整流电路不能采用电容滤波。

由于二极管与晶闸管相比,其承受浪涌过载电流的能力比晶闸管强。另外晶闸管的安全还受通态电流临界上升率(di/dt)的制约,通态电流的上升率过大同样会导致元件损坏。如果晶闸管整流电路也采用电容滤波,那么元件一导通就要向电容器充电,其充电电流的大小与电源和电容器之间的电压差及电源和电容构成回路的电抗有关。当压差较大、电抗较小时该电流会很大,而且上升速率很快,当超出元件的承受能力时会损坏元件,因此晶闸管整流电路一般不采用电容滤波。

选择题
写作题

阅读下面的短文,然后按要求写一篇150词左右的英语短文。

There are all kinds of stress in our daily lives such as stress from work, stress from study and stress from examinations. How to manage stress is thus a very important problem that we have to deal with properly. I think stress itself doesn’t exist. It’s only because we consider things to be bad and regard all of them as our own fault and won’t forgive ourselves. As we all know, there is nothing you can do without error. So it’s impossible to expect everything to be perfect. If we have done our best,  although not successfully, there is nothing to regret. And we don’t need to blame ourselves continuously. In fact we have done a quite good job. Then we will feel the stress less. We will stay healthy and do well in the future. Eventually we will be successful.

[写作内容]

1.概括短文内容要点,该部分的字数大约30词左右;

2.就“如何化解心理压力”这个主题发表你的看法,至少包括以下的内容要点,该部分的字数大约120词左右。

a)简述你生活学习中遇到过造成较大心理压力的困难;

b)你是如何化解心理压力的;

c)谈谈你对化解心理压力的体会。

[写作要求]

你可以参照阅读材料的篇章结构、有关内容,但不得直接引用原文中的句子。

[评分标准]

概括准确、语言规范、内容合适、篇章连贯。

______________________________________________________________________________________________________________________________________________________________

______________________________________________________________________________________________________________________________________________________________

______________________________________________________________________________________________________________________________________________________________

______________________________________________________________________________________________________________________________________________________________

_________________________________________________________________________________