题干

如图所示电路中,电源的电动势为E,内阻为r,各电阻阻值如图所示,当滑动变阻器的滑动触头P从a端滑到b端的过程中,下列说法正确的是

A:电压表的读数U先减小,后增大

B:电流表的读数I先增大,后减小

C:电压表读数U与电流表读数I的比值U/I不变

D:电压表读数的变化量ΔU与电流表读数的变化量ΔI的比值ΔU/ΔI不变

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D

同类题3

阅读理解

    When people find something valuable and return it to its owner,they are often given a reward.This is because the person not only found what was lost but also spent time finding its owner or taking it to the police station.

    There was once a young boy who found a woman's purse in a shopping center.Inside the purse there was some money and the woman's driving license.Her name and address were printed on the license,so the boy knew where she lived.That evening he went to her house and knocked on her door.When she opened it,he said,“I found your purse,''and handed it to her.

    “Thank you very much,”she said.She opened her purse and took out all the money.She wanted to give the boy a small reward,but there were only bills of$20 in the purse and she thought that$20 was too much to give the boy.“I'm sorry,”she said. “but I don't have any small change to give you.”

    The boy said,“That's all right,”and he went away.

    A few days later he found another woman's purse.It also had her driving license in it,so he knew where she lived.He went to her house and said.“l found your purse ,”and handed it to her.

    “Thank you very much,"she said.  She opened her purse and took out all her money.

    “That‘s strange,”she said.“Before I lost my purse l had a $100 bill and a $20 bill in it.Now I have a $100 bill ,a $10 bill and two $5 bills.''

    “Yes,"the boy said,and smiled.