单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,测量电表的内阻,电流表内阻的测定,伏安法测电压表电阻,比较法测电压表电阻,003.,南京师大物理之友电学综合,(,一,)14,014.,山东泰安市,07,年第一轮质量检测,10,042.,08,年苏、锡、常、镇四市教学情况调查（一）,11,测量电表的内阻,电流表内阻的测定,（,1,）电流表的满偏电流,Ig,、内电阻,Rg,和满偏电压,Ug,三者的关系,Ug=Ig Rg,（,2,）电流表内电阻的测定,半偏法（不计电源内阻）,G,S,1,S,2,R,1,R,2,若,R,1,R,2,则,R,g,=,R,2,伏安法测电压表电阻,电压表是一个能够显示自身电压的特殊电阻，因此，可以用一个安培表测量其电阻。,V,A,读出,电压表和电流表的示数,U,和,I,，则,比较,法测电压表电阻,甲图中的电压表的电压为,U,1,;,V,R,V,甲,乙,乙图中的电压表的电压为,U,2,R,为已知大电阻,(,不计电源内阻,),003.,南京师大物理之友电学综合,(,一,)14,、,将一只最大量程为,3V,的电压表、一只最大量程为,1mA,的电流表、一只最大阻值为,20,的滑线变阻器、一只开关和,4.5V,的电池按图连接测量电压表的内阻,（估计为,10,3,的数量级）,闭合开关，,能否测出？简说理由。如若不能，,请设计出最简单的方案，写出所,需器材与做法。,A,V,P,解：,不能测出电压表的内阻。因为滑动变阻器的阻值太小，会超出电表的量程。,最简单的方案是需要一根导线。,接法如图所示,A,V,P,014.,山东泰安市,07,年第一轮质量检测,10,13.,测量一块量程已知的电压表的内阻，器材如下：,A,待测电压表（量程,3,V,，内阻未知）一块,B,电流表（量程,3A,，内阻,0.01,）一块,C,定值电阻,R,0,（阻值,5k,，额定电流,0.5,A,）一个,D,电池组（电动势小于,3,V,，内阻不计）一个,E,多用电表一块,F,开关,K,1,、,K,2,G,导线若干,有一同学利用上面所给器材，进行如下实验操作：,(1),用多用电表进行粗测：多用电表电阻档有,3,种倍率，分别是,100,、,10,和,1,。该同学选择,10,倍率，用正确的操作方法测量时，发现指针偏转角度太小。为了较准确地进行测量，,应重新选择,倍率。,重新选择倍率后，刻度盘上的,指针位置如图所示，那么测量,结果大约是,k,。,1k,100 50 30 20 15 10 5 0,100,3.0,（,2,）为了更准确的测出该电压表内阻的大小，该同学设计了如图甲、乙两个实验电路。你认为其中较合理的是,（填,“,甲,”,或,“,乙,”,）电路。其理由是：,。,（,3,）用你选择的电路进行实验时，需要直接测量的物理量,；,用上述所测各量表示电压表内阻，其表达式应为,R,V,。,A,V,K,1,甲,V,K,2,K,1,R,0,乙,乙,因为甲图中流过电流表的电流太小,读数误差比较大,K,2,闭合与断开时电压表的读数,U,1,、,U,2,电压表内阻的表达式为,042.08,年苏、锡、常、镇四市教学情况调查（一）,11,11,现要尽可能精确地测量一量程为,3V,的电压表的内阻（内阻约,5000,）,.,（,1,）需要哪些实验器材？请写出主要器材的规格，画出实验电路图并简要叙述测量电压表内阻的方法,.,（,2,）实验室有,00.6A3A,规格的常用电流表和,03V15V,规格的常用电压表，其内阻均未知，另外有电源、滑动变阻器（最大阻值约为,50,）、开关、导线这些器材，若只选用这些器材，能否达到实验目的,?,请说明理由,.,解：（,1,）,还要毫安表（量程是,1mA,）、电源（电动势,3V,）、开关、导线,原理图如右图,mA,V,测量方法：,读出电压表的读数是,U,和毫安表的读数,I,，,则电压表的内阻可表示为,R,V,=U/I,(2),不能，因为电压表的内阻太大，无法精确测量其电流值。,Prepositions,Unit 1 Living with technology,Prepositions are words that are used before a noun or a noun phrase to show time,place,movement,etc.,A preposition can also be used before a verb in the ing form.,List all the prepositions in the story and think how they are used.,My family will move to a new flat.We need a lot of new household appliances before we can move in.Last Saturday,we went to a department store.The household appliances section is on the fifth floor.,We first bought a fridge and an electric rice cooker.My parents suggested we buy a microwave oven so that we can save a lot of time reheating food.,Then we bought a washing machine.After that,a vacuum cleaner came into our package as it is useful for keeping our house clean.We had a tiring but happy day.,My family will move,to,a new flat.We need a lot of new household appliances,before,we can move in.Last Saturday,we went,to,a department store.The household appliances section is,on,the fifth floor.We first bought a fridge and an electric rice cooker.,My parents suggested we buy a microwave oven so that we can save a lot of time reheating food.,Then we bought a washing machine.,After that,a vacuum cleaner came,into,our package as it is useful,for,keeping our house clean.We had a tiring but happy day.,Prepositions are used before a noun or a noun phrase.And when a verb is used after a preposition,it is usually used in its,-ing,form.,Read the dialogue on Page 8 and fill in the blanks with proper prepositions.,Answers,(1)for (2)at (3)until (4)by (5)during (6)to,Prepostions,Prepostions of time,at,in,for,by,since,during,before,after,from,until,Prepostions of place,at,in,on,above,against,behind,between,under,oppostite,Prepostions of movement,Across,along,down,into,off,over,round,through,uder,up,表示时间的,at,in,on,at,表示片刻的时间，或者说时间点,at 8 oclock,，常用词组有：,at noon,at night,at midnight,at the end of,at that time,at the beginning of,at the age of,at Christmas,at New Year,等。,in,表示一段的时间，,in the morning,in the afternoon,in the evening,in October,in 1998,in summer,in the past,in the future,等。,on,总是跟日子有关，,on Monday,on Christmas morning,on the following,on May Day,on,a warm morning,等。,表示时间的,since,和,from,since,表示从过去到现在的一段时间的过程，常与现在完成时连用。,from,表示从时间的某一点开始，不涉及与现在的关系。一般多与现在时、过去时、将来时连用。,如：,I hope to do morning exercises from today.,We have not seen each other since 1995.,表示时间的,in,和,after,：,两者都表示“在（某个时间）之后，区别在于,in,表示“在（一段时间）之后”，而,after,则表示“在（某一具体时间点之后）”，,in,短语和将来时态连用，,after,短语和过去时态或将来时态连用。,如：,Well be back in three days.,After seven the rain began to fall.,What shall we do after graduation?,注意：,after,有时也可以表示在一段时间之后（常用在过去时里）。,如：,After two months he returned.,表示地理位置的,in,on,to,in,表示在某范围内，,on,指与什么毗邻，,to,指在某环境范围之外。,Changchun is in the northeast of China.,Mongolia is on the north of China.,Japan is to the east of China.,under/over,below/above,below,是,on a lower level than,的 意思,表示在下方位置的某物,.,不强调直上直下,反义词是,above,.,under,有,directly below,的含义,表示垂直在下方,反义词是,:,over.,表示“穿过,”,的,through,和,across,through,表示从内部通过，与,in,有关；,across,则表示从一端至另一端在表面上的通过，与,on,有关。,over,指从一个物体的一边到另一边的越过,Water flows through the pipe.,The old man walked across the street.,toward(s),to,for,to,和,toward(s),用来表示静态的方向,可以换用,但和表示位置转移的动词如,:go,come,move,run,return,walk,等连用是,to,有到达之意,而,toward(s),只表示运动方向,无到达之意,.,for,一般用语动词,leave,sail,start,及短语,set off,set out,start out,start off,等短语后表示方向,.,R