The median resistance is 1500 ohm, two ammeters with 1mA measuring range, one with 250 ohm internal resistance and the other with 100 ohm internal resistance, which one is better

The median resistance is 1500 ohm, two ammeters with 1mA measuring range, one with 250 ohm internal resistance and the other with 100 ohm internal resistance, which one is better

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The ohmmeter with a median resistance of 1500 Ω is designed. There are two ammeters with a range of 1mA, with internal resistances of 250 Ω and 100 Ω respectively

The mean value resistance of ohmmeter is the sum of internal resistance Rg, zero setting resistance (sliding rheostat) R0 and internal resistance R of battery
If you want to design an ohmmeter with a median resistance of 1500 Ω, I think you can choose either one of the two ammeters with a range of 1mA and an internal resistance of 250 Ω and 100 Ω (because the resistance value of the sliding rheostat you want to choose is 1500-250 = 1250 Ω or
1500-100 = about 1400 Ω, the difference is not much. The internal resistance of the battery is small, which can be omitted when selecting equipment). The electromotive force of the battery is
E = I full * r middle = 1 * 10 ^ (- 3) * 1500 = 1.5 v
If from the point of view of convenient adjustment, it is better to choose an ammeter with 250 ohm internal resistance, because the resistance value of the sliding rheostat used is slightly smaller, and it is more convenient to adjust the zero point (the pointer will not swing greatly, and it is easy to adjust the zero point)
Note: when the median resistance and full bias current of ohmmeter are determined, the scale mark is determined