将阻值为5Ω的电阻接到内阻不计的交流电源上，电源电动势随时间变化的规律如图所示．下列说法正确的是（ ）
A．电路中交变电流的频率为25 Hz
B．通过电阻的电流为
A2 2
C．电阻消耗的电功率为2.5 W
D．用交流电压表测得电阻两端的电压是5 V
A、由图可知：f=
=1 T
Hz=25Hz，故A正确；1 4×10-2
B、根据欧姆定律，I=
=U R
A，故B正确2 2
C、根据功率，P=
=2.5W，故C正确．U2 R
D、该电源电动势的有效值为U=
=EM 2
V，电压表的示数为有效值，故D错误；5 5 2
故选ABC．
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| The 50-year-old farmer (农民), Wu Yulu is quite different from the others at his village. He is the 1 of 38 handmade robots. He has been 2 to show his robots at the opening ceremony of the Shanghai World Expo. Born in a 3 family, he did not have the opportunity to go to school. But even as a child, he knew he wanted to make machines. “I think 4 machines is a talent I was born with,” he said.In 1987, he finally finished his 5 robot that could walk like a man. He named it “Wu No. 1.” 6 , his experiments (实验) have not been without danger. One of his fingers was injured in 1989. And in 1999, his house was 7 by fire. In 2003, Wu and his robots were invited to perform in the Great Hall of the People in Beijing, and in 2009, his robots were on 8 along with the Chinese Shenzhou spaceships.Wu's latest dream is to invent robots 9 can help people in daily life. He will invent robots to help the disabled or look 10 children. | ||||
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