题干

在图所示的电路中,电源电压为10伏且不变.定值电阻R1的阻值为10欧,滑动变阻器R2上标有“2A”字样.闭合电键S


①求通过R1的电流I1

②通电10秒,求电流通过R1所做的功W1

③在电路安全工作的情况下,移动变阻器R2的滑片,电路消耗的最大功率恰为最小功率的2倍,求变阻器的最大阻值.

上一题 下一题 0.0难度 选择题 更新时间:2018-04-19 10:08:22

答案(点此获取答案解析)

解:由电路图可知,R1与R2并联.

①因并联电路中各支路两端的电压相等,

所以,通过R1的电流:

I1= UR1

同类题1

完形填空

    Workers aren't allowed to go into a big underground computer center until they step up to a machine that takes a quick picture of the tiny blood vessels (血管) inside their eyes.

    If the machine can't 1 the picture with images in its computer, the worker is stopped by security guards (保安员).

    Each person has his own way of blood vessels in his or her2.And unlike a key, the way can't be3.Old-fashioned keys and locks may soon be things of the past.High-tech security devices (安全装置) are being fixed at military (军事的) bases, computer centers and banks.Companies that 4 the machines say they'll someday be used in people's homes and cars.

    Already, a Japanese company has fixed ways that recognize (识别) people's fingerprints in 360 new homes.The machines open the doors only for the 5of the houses.The new security ways are selling well because thieves and robbers are getting better at breaking into buildings and computers that are 6 by keys and locks.Since nobody can steal or copy a fingerprint, or one's eyes, the new machines are 7.

    Other new machines recognize one's voice.Two American companies use 8 machines to keep an eye on their computers.Inexpensive voice-recognition machines may someday take the place of locks on cars.The doors would open only for the owners.The machines would 9 the owners as little as $270.Although the up-to-date machines are amazing, scientists must still solve a serious problem.How will a boy borrow his dad's car without borrowing his dad's 10?