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I've been studying experimental electrodynamics and I needed to describe an experiment to find the resistance of an ammeter if I just have the ammeter together with one voltmeter and a protection resistance. My idea was the following: since the ammeter has much less resistance than the voltmeter we connect them in paralel and connect this in series with a protection resistance connected to the battery.

The idea is that the current will be reduced by the protection resistance avoiding damages to the ammeter. Then the current will divide and a much greater part will flow through the ammeter. Since the ammeter and the voltmeter are in parallel the voltage seen in the voltmeter is the same on both devices, and the ammeter will show the current that flows through it so that we can use Ohm's Law to find it's resistance: $R=V/I$. If we knew then the errors of the ammeter and of the voltmeter we could propagate to find the error in the resistance.

Is this correct? Is this a valid way to measure the resistance of the ammeter? Thanks very much in advance for the help.

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closed as too localized by Manishearth May 10 '13 at 6:14

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up vote 2 down vote accepted

Your reasoning is correct. And as a bonus: to measure the resistance of the voltmeter, you put it in series with the ammeter.

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