题目

如图电路中，电源电压保持不变，当开关S闭合，滑动变阻器的滑片P向右移动时，电流表和电压表的示数变化情况分别为（ ） A．电流表的示数变小，电压表的示数变大 B．电流表的示数变大，电压表的示数变小 C．电流表的示数变小，电压表的示数不变 D．电流表的示数变小，电压表的示数变小 答案：C【考点】欧姆定律的应用；滑动变阻器的使用． 【分析】由电路图可知，R1和R2并联，电压表测量电源电压，电流表测干路电流；当滑动变阻器的滑片P向右移动时，电源电压保持不变，电压表的示数不变；根据欧姆定律可知通过R1的电流不变，但通过R2的电流变小，根据并联电路的电流特点可知电流表Since the first Earth Day in 1970,American have gotten a lot “greenter” toward the environment . “We didn’t know at that time there even was an environment,let alone that there was a problem with it,”says Bruce Anderson,president of Earth Day USA.But what began as nothing important in public affairs has grown into a social movement .Business people,political leaders, university professors,and especially millions of grass-roots Americans are taking part in the movement. “The understanding has increased many ,many times,”says Gaylord Nelson,the fromer govermor from Wisconsin,who thought up the first According to US government reports , emissions (排放)from cars and trucks have dropped from 10.3 million tons a year to 5.5 tons .The number of cities producing CO beyond the standard has been reduced from 40 to 9 .Although serious problems still remain and need to be dealt with , the world is a safer and healthier place .A kind of “Green thinking ” has become part of practices .Great improvement has been achieved .In 1988 there were only 600 recycling programs ,; today in 1995 there are about 6,600 .Advanced lights ,motors , and building designs have helped save a lot of energy and therefore prevented pollution . Twenty –five years ago , there were hardly any education programs for environment .Today , it’s hard to find a public school , university , or law school that does not have such a kind of program .” Until we do that , nothing else will change! ” say Bruce Anderson .小题1:According to Anderson , before 1970, Americans had little idea about ___A．the social movement B．recycling techniquesC．environmental problemsD．the importance of Earth Day小题2:Where does the support for environmental protection mainly come from?A．The grass –roots level B．The business circle C．Government officialsD．University professors小题3:What have Americans achieved in environmental protection ?A．They have cut car emissions to the lowest B．They have settled their environmental problems C．They have lowered their CO levels in forty cities.D．They have reduced pollution through effective measures .小题4:What is especially important for environmental protection according to the last paragraph ?A．Education B．Planning C．Green living D．CO reduction