两只相同的白炽灯L1和L2,分别与电容器C和电感线圈L串联,接在如图所示的电路中

题型:不定项选择

问题:

两只相同的白炽灯L1和L2,分别与电容器C和电感线圈L串联,接在如图所示的电路中。将a、b接在电压最大值为Um、频率为f的正弦交流电源E1两极之间时,两只灯泡都发光,且亮度相同。若更换一个新的正弦交流电源E2后,灯L1的亮度比原来高。则新电源E2的电压最大值和频率可能是

[ ]

A.最大值仍为Um,而频率大于f

B.最大值仍为Um,而频率小于f

C.最大值大于Um,而频率仍为f

D.最大值小于Um,而频率仍为f

考点:电容器对交变电流的作用电感器对交变电流的作用
题型:不定项选择

Class regulations require ____ is the last to leave the Classroom ____ off all the lights. [ ]

A. who; should turn

B. whomever; turn

C. whoever; turning

D. whoever; turn

题型:不定项选择

将一定质量的铁粉和锌粉的混合物加入CuSO4溶液中,反应结束后过滤,滤液为无色,下列对滤液所含溶质和滤渣成分的判断中,正确的是

A.滤液中一定含有ZnSO4

B.滤渣中一定没有铁粉

C.滤液中可能含有FeSO4

D.滤渣中一定有锌粉

题型:不定项选择

前列腺增生的MRI表现主要为TWI上__________________,然而信号正常。

题型:不定项选择

根据上图,下列说法正确的是()。

A.“十五”时期粮食产量逐年上升

B.“十五”时期粮食产量年增长率逐年提高

C.“十五”时期粮食产量最高的年份是2004年

D.“十五”时期粮食产量年增长率最高的年份是2004年

题型:不定项选择

Fatigue is one of the most common complaints brought to doctors, friends, and relatives. You’d think in this era of labor-saving and convenient transportation that few people would have reason to be so tired. The causes of modern-day fatigue are diverse and only rarely related to excessive physical exertion. Today, physicians report, tiredness is more likely a consequence of underexercise than of wearing yourself down with overactivity.

Physical fatigue is the well-known result of overworking your muscles. (46) Physical fatigue is usually a pleasant tiredness, such as that which you might experience after playing a hard set of tennis, chopping wood, or climbing a mountain. The cure is simple and fast: You rest, giving your body a chance to get rid of accumulated waste and restore muscle fuel.

(47) Illness induced fatigue is a warning sign or consequence of some underlying physical disorder, perhaps the common cold or flu or something more serious like cancer, while other symptoms are present that often suggest the true cause. Even after an illness passed, you’re likely to feel dragged out for a week or more. (48) Take your fatigue as a signal to go slow while your body has a chance to recover fully even if all you had was a cold. Pushing yourself to resume full activity too soon will certainly prolong your period of fatigue.

Emotional problems and conflicts, especially depression and anxiety, are by far the most common causes of prolonged fatigue. When such feelings are not expressed openly, they often come out as physical symptoms, with fatigue as one of the most common manifestations. (49) Understanding the underlying emotional problem is the crucial first step toward curing psychological fatigue and by itself often results in considerable lessening of the tiredness. Professional psychological help or career or marriage counseling may be needed.

There is a great deal you can do on your own to deal with both severe prolonged fatigue and those periodic washed-out feelings. You might try to do moderate exercise. (50) Contrary to what you may think, exercise enhances, rather than drains, engery and helps you to resist fatigue by increasing your body’s ability to handle more of a workload. At the end of a day exercise can relieve accumulated tensions, give you more energy in the evening, and help you sleep more restfully.

(49) Understanding the underlying emotional problem is the crucial first step toward curing psychological fatigue and by itself often results in considerable lessening of the tiredness.

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