问题 问答题 简答题

如何区分系统发生的振荡属异步振荡还是同步振荡?

答案

参考答案:

异步振荡其明显特征是:系统频率不能保持同一个频率,且所有电气量和机械量波动明显偏离额定值。如发电机、变压器和联络线的电流表、功率表周期性地大幅度摆动;电压表周期性大幅摆动,振荡中心的电压摆动最大,并周期性地降到接近于零;失步的发电厂间的联络的输送功率往复摆动;送端系统频率升高,受端系统的频率降低并有摆动。

同步振荡时,其系统频率能保持相同,各电气量的波动范围不大,且振荡在有限的时间内衰减从而进入新的平衡运行状态。

阅读理解

(2013·高考浙江卷,C)The baby monkey is much more developed at birth than the human baby.Almost from the moment it is born,the baby monkey can move around and hold tightly to its mother.During the first few days of its life the baby will approach and hold onto almost any large,warm,and soft object in its environment,particularly if that object also gives it milk.After a week or so,however,the baby monkey begins to avoid newcomers and focuses its attentions on“mother”—the real mother or the mother­substitute(母亲替代物).

During the first two weeks of its life warmth is perhaps the most important psychological(心理的)thing that a monkey mother has to give to its baby.The Harlows,a couple who are both psychologists,discovered this fact by offering baby monkeys a choice of two types of mother­substitutes—one covered with cloth and one made of bare wire.If the two artificial mothers were both the same temperature,the little monkeys always preferred the cloth mother.However,if the wire model was heated,while the cloth model was cool,for the first two weeks after birth the baby monkeys picked the warm wire mother­substitutes as their favorites.Thereafter they switched and spent most of their time on the more comfortable cloth mother.

Why is cloth preferable to bare wire?Something that the Harlows called contact(接触)comfort seems to be the answer,and a most powerful influence it is.Baby monkeys spend much of their time rubbing against their mothers’ skins,putting themselves in as close contact with the parent as they can.Whenever the young animal is frightened,disturbed,or annoyed,it typically rushes to its mother and rubs itself against her body.Wire doesn’t “rub” as well as does soft cloth.Prolonged(长时间的)“contact comfort” with a cloth mother appears to give the babies confidence and is much more rewarding to them than is either warmth or milk.

According to the Harlows,the basic quality of a baby’s love for its mother is trust.If the baby is put into an unfamiliar playroom without its mother,the baby ignores the toys no matter how interesting they might be.It screams in terror and curls up into a furry little ball.If its cloth mother is now introduced into the playroom,the baby rushes to it and holds onto it for dear life.After a few minutes of contact comfort,it obviously begins to feel more secure.It then climbs down from the mother­substitute and begins to explore the toys,but often rushes back for a deep embrace(拥抱)as if to make sure that its mother is still there and that all is well.Bit by bit its fears of the new environment are gone and it spends more and more time playing with the toys and less and less time holding onto its “mother”.

小题1:Psychologically,what does the baby monkey desire most during the first two weeks of its life?

A.Warmth.

B.Milk.

C.Contact.

D.Trust.小题2:After the first two weeks of their life,baby monkeys prefer the cloth mother to the wire mother because the former is________.

A.larger in size

B.closer to them

C.less frightening and less disturbing

D.more comfortable to rub against小题3:What does the baby monkey probably gain from prolonged“contact comfort”?

A.Attention.

B.Softness.

C.Confidence.

D.Interest.小题4:It can be inferred that when the baby monkey feels secure,________.

A.it frequently rushes back for a deep embrace when exploring the toys

B.it spends more time screaming to get rewards

C.it is less attracted to the toys though they are interesting

D.it cares less about whether its mother is still around小题5:The main purpose of the passage is to ________.

A.give the reasons for the experiment

B.present the findings of the experiment

C.introduce the method of the experiment

D.describe the process of the experiment

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