班别: 姓名: 分数: 一、想一想,填一填(每空1分,共20分) 1.要在一段电路中产生电流,它的两端就要有_______。电阻是导体对电流的_____作用,50Ω的实验用的小灯泡接入电路中,若开关没有闭合,则它的电阻是________。 2.滑动变阻器是靠改变电阻线在电路中的_________来改变电阻,从而改变电路中的电压和电流,一个滑动变阻器上标有“2.5A,50Ω”的字样,其中2.5A表示_________________大量实验表明_______ 的电压一般对人体是安全的。 3.电流通过电机产生的热量是有害的,因此要在电动机外壳设计________,在电视机后盖上设计________。但家用电器若长时间停用,应隔一段时间通电一次,这样做对维修家电有好处。 4.如图1所示电路中,AB两端电压U=8V,且保持不变,如果R2两端电压U2=2V,R1=4Ω,那么通过R1的电流是________A。若要通过它的电流 图1 为0.4A,必须把导体两端电压调到________。小军上月家中电能表的示数为 ,若他家有40瓦灯6盏,100瓦电视机一台,平均每天使用4小时,本月共30天,本月底电能表示数为 。 5.用电器R1和R2上都标有“6V”字样,已知它们的电流随电压变化的图象如 图2所示。利用该图象可求出用电器R1的额定功率是______W;若把R1和 R2 并联在电源电压为6V的电路中工作,则通过R2的电流是______A。电阻R1的阻值是______Ω。 6.“6V、3W”的小灯泡要接在10V的电源上使它正常发光,应串联一个阻值为______Ω的电阻。若它接在4V的电源上时,其实际功率为________W。 7.将下列物质①铅笔芯;②玻璃砖;③水银;④汽油;⑤铜丝;⑥橡皮分为两类:一类包括________,其共同特征是导体;一类包括________,其共同特征是绝缘体。 下载地址:
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