问题 选择题

如图,电源电压和A、B两灯的电阻均不变.若滑动变阻器R的滑片向右滑动,则(  )

A.A、B两灯均变亮

B.A、B两灯均变暗

C.A灯变亮,B灯变暗

D.A灯变暗,B灯变亮

答案

滑动变阻器R的滑片向右滑动时,接入电路的电阻增大,变阻器与A灯并联的电阻增大,外电路总电阻增大,总电流减小,电源的内电压减小,则路端电压增大.A通过B灯的电流即为总电流,所以可知B灯变暗.路端电压增大,B灯的电压减小,电源的电压不变,则变阻器与A灯并联的电压增大,A灯变亮.故C正确.

故选C

单项选择题

Generally speaking, a British is widely regarded as a quiet, shy and conservative person who is (1) only among those with whom he is acquainted. When a stranger is at present, he often seems nervous, even (2) . You have to take a commuter train any morning or evening to (3) the truth of this.

Serious-looking businessmen and women sit reading their newspapers or dozing in a corner; hardly anybody talks, since to do so would be considered quite (4) .

(5) , there is an unwritten but clearly understood code of behavior which, once broken, makes the offender immediately the object of (6) .

It has been known as a fact that a British has a (7) for the discussion of their weather and that, if given a chance, he will talk about it (8) .

Some people argue that it is because the British weather seldom (9) forecast and hence becomes a source of interest and (10) to everyone.

This may be so. (11) a British cannot have much (12) in the weathermen, who, after promising fine, sunny weather for the following day, are often proved wrong (13) a cloud over the Atlantic brings rainy weather to all districts! The man in the street seems to be as accurate — or as inaccurate — as the weathermen in his (14) .

Foreigners may be surprised at the number of references (15) weather that the British (16) to each other in the course of a single day. Very often conversational greetings are (17) by comments on the weather. “Nice day, isn’t it” “Beautiful!” may well be heard instead of “Good morning, how are you” Although the foreigner may consider this exaggerated and comic, it is (18) .pointing out that it could be used to his advantage. If he wants to start a conversation with a British but is at a loss to know (19) to begin, he could do well to mention the state of the weather. It is a safe subject which will (20) an answer from even the most reserved of the British.

9()

A.follows

B.obeys

C.defies

D.supports

选择题