问题 选择题

把一个灯泡接到某电压不变的电源两端,灯泡的功率为100W。将一个电阻R与这只灯泡串联后接到同一电源两端,灯泡的功率为64W,设灯丝电阻不变。则电阻R消耗的功率是 

A.8W

B.10W

C.16W

D.36W

答案

答案:C

题目分析:设电路中只接一个灯泡时电流为,则,电阻R与灯泡串联时电流为,则

则:   

由于电源电压不变,电流与总电阻成反比,所以  

在串联电路中,则

完形填空
A woman is going shopping. She is going      boat. The boat is going across(穿过)the river. Her basket is empty(空的). Oh dear! Look! Her basket is in the      .“Help!”she says.“Look! My basket is in the river.”
A boy sees the basket. He says, “Don’t worry! I can      it! I’m a very good swimmer.” He takes _  _his shoes and shirt. “Look      my shirt and shoes, please!” he says and then jumps _____ the river.  A      sees the basket. “I can go by basket!” it thinks. It gets to the basket. The boy      in the river. “Where’s the basket?” he calls:“It’s ____ there!” calls the woman. “It’s behind you!” It’s      that duck! The boy gets to the basket.“Go away!” he says __  __ the duck. The duck      out of the basket and swims away. The boy takes the basket to the land. “Oh, thank you!” says the woman. “Thank you very much!”
“Not at ____!” says the boy.“      you like to give me my shirt and shoes?”
“Yes, here you are. Oh, what’s in the basket? It’s the duck’s      .”
小题1:
A.onB.inC.byD.to
小题2:
A.waterB.boatC.shipD.tree
小题3:
A.cleanB.buyC.doD.get
小题4:
A.onB.inC.offD.up
小题5:
A.afterB.atC.forD.like
小题6:
A.ontoB.atC.intoD.off
小题7:
A.dogB.chickenC.duckD.monkey
小题8:
A.is fishingB.is swimming C.is playingD.is flying
小题9:
A.underB.in front ofC.overD.behind
小题10:
A.besideB.underC.onD.behind
小题11:
A.atB.withC.toD.for
小题12:
A.climbsB.comesC.jumpsD.walks
小题13:
A.onceB.itC.allD.work
小题14:
A.AreB.DoC.WouldD.Could
小题15:
A.meatB.hairC.handD.Egg
单项选择题