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1995年高考物理试题的第11题如下:如图1表示一交流电的电流随时间而变化的图象,此交流电的有效值是 A.52~(1/2)安 B.5安 C.3.5安 D.3.52~(1/2)安 分析与解:设该交流电对阻值为R的电阻供电。一周期内产生的焦耳热Q=I_1~2Rt_1+I_2~2Rt_2。根据等效原理,Q=I~2R(t_1+t_2),因为t_1=t_2=0.01秒,I_1=42~(1/2)安,I_2=32~(1/2)安,所以该交流电有效值I=(I_1~2+I_2~2)/2~(1/2)=5安。 在考试中,不少考生由于对交流有效值的概念理解不够透彻,只是机械地记住了书本上关于正弦交流
The 11th problem of the 1995 college entrance examination physics test questions is as follows: Figure 1 shows the image of an alternating current current varying with time. The effective value of this alternating current is A.52~(1/2) Ann B.5 Ann C.3.5 An D.3.52 ~ (1/2) Ann analysis and solution: Let this alternating current supply power to the resistance of R. The Joule heat generated during one cycle is Q=I_1~2Rt_1+I_2~2Rt_2. According to the equivalence principle, Q=I~2R(t_1+t_2) because t_1=t_2=0.01 seconds, I_1=42~(1/2)ampere, I_2=32~(1/2)ampere, so the AC power is effective. The value I=(I_1~2+I_2~2)/2~1/2=5A. In the examination, many candidates were not thorough enough to understand the concept of AC RMS, but mechanically remembered the book about sinusoidal communication.