推荐回答（1个）
The Resistance Of Ammeter Is Low
If The Ammeter Connect In Parallel
It May Cause Short Circuit
So If The Resistance Is Low
It Must Connect In Series To Make Sure That It Can't Upset The Circuit But Still Can Measure The Current
电流表必须用串联，是因为： 1) ammeter 是量度电路上使用的电流 -Amp，若果并联便型成分流，并不是量度的电流数据。 2) 由于 ammeter 的内阻大低，并联便好像型成一个短路，引致烧表。
Simply speaking
ammeter is an instrument used to measure electric current
and electric current is a flow of charges. Therefore
if you wish to measure the "flow of charges" at a point on an electric circuit
you must con an instrument at that point in order to "catch this flow of charges". Obviously
the ammeter has to be inserted at that particular point to let charges flow through it. This is in fact a series conection.
在直流的量度来说，电压表和电流表的表头系同一样野，只视乎如何将它与附助电路配合，之后才能成为电压表或电流表，其实最终对表头来讲都系量度电压，电压表用分压电阻，而电流表就系量度串联于电路中的电阻两端的电压差，从而显示出电流状况，故直流电流表必须串接于电路上才可工作。 至于量度交流电流，会利用磁场的强弱，通过磁感应（就如一个小型变压器，初级是所测电器的一条回路，次级接至钳表电路）及再整流后通过表头显示出来。
电流表要串联在电路上既系直接电流表，其实仲有含分流器既电流表，含互感器电流表，钳形电流表，叉形电流表等好多种。 2009-04-21 22:34:01 补充： 为什么？ 只有一个理由，要量电流量。
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