问题 填空题

如图所示的电路中,电源电压为6V,开关S断开时,电流表的示数为0.3A,开关S闭合时电流的示数为0.5A,则R2的阻值为______Ω,R1消耗的功率是______W,2秒种内整个电路消耗的电能是______J.

答案

分析电路图,开关S断开时:I2=0.3A,开关S闭合时:I=0.5A,

∵接在同一电源上,开关开闭对R1无影响(电流不变)

∴I1=I-I2=0.5A-0.3A=0.2A

R2=

U
I2
=
6V
0.3A
=20Ω

P1=UI1=6V×0.2A=1.2W

W=UIt=6V×0.5A×2s=6J

故答案为:20,1.2,6

完形填空
Never try to work when you are very hungry .If you   36  your homework right after school, you may want to have a snack before getting to work. Always do your homework       37   you get tired.____38____wait until very late in the evening ,or the assignment(功课)will seem much  39  than it really is .Break your time into manageable(易处理的) period .If you have more than  40,give yourself a break after an hour .On the other hand ,don't break it up _41  that you can’t get anything done .You should be able to work at least half an hour at a time  42  .Don't put it off  43   the last minute .If you put off doing your homework ,you will always think of it ,and you won’t enjoy your  44   so much .If you put it off until the end of the week  until right before a test ,you will have too much work to do for the exam .A little bit each night ,enough to keep up with what is happening each day in school ,will take the fear out of tests and keep you on top of it all .Do your hamework__45  every day .This will help you make it a habit .It will make it easier to do ,and it will make free time more enjoyable as well.
小题1:
A.decided doingB.decide to doC.have doneD.did
小题2:
A.afterB.whenC.beforeD.because
小题3:
A.NotB.PleaseC.AlwaysD.Don't
小题4:
A.hardB.harderC.easyD.easier
小题5:
A.one hour workB.an hour work
C.an hour's workD.a work of an hour
小题6:
A.so muchB.so 1ittleC.so oftenD.so well
小题7:
A.without stoppingB.with stop
C.stopD.without stop
小题8:
A.forB.onC.atD.until
小题9:
A.lunchB.free timeC.mealsD.snack
小题10:
A.at a timeB.at the same time
C.onceD.in the same way
选择题