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1998年高考物理试卷的第20题:用图1所示电路测定未知电阻R_x的值,图中电源电动势未知,电源内阻与电流表的内阻均可忽略不计,R为电阻箱.(1)若要测得R_x的值,R至少取_____个不同数值.(2)若电流表每个分度表示的电流值未知,但指针偏转角度与通过的电流成正比,则用此电路测R_x值时,R至少需取
The 20th item of the 1998 college entrance examination physics test paper uses the circuit shown in Fig. 1 to determine the value of the unknown resistor R_x. The figure shows that the power EMF is unknown. The internal resistance of the power supply and the internal resistance of the ammeter are negligible. R is the resistance box. (1) To measure the value of R_x, R must take at least _____ different values. (2) If the current value represented by each index of the ammeter is not known, but the pointer deflection angle is proportional to the passing current, use this circuit to measure R_x. At least one R must be taken