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Suppose you have the following circuit: Circuit!

Where R1 = 1 kΩ, R2 = 2 kΩ, R3 = 3 kΩ, R4 = 4 kΩ, R5 = 5 kΩ, Vs = 5V. The voltage in the branch with R5 is then 5 I where I over R5 is .064A.

Suppose you put a voltmeter to measure Vab which is the voltage from node Va to node Vb. This would just be the voltage in the branch: 5 * .064, if im not mistaken.

But what if you put an ammeter in to find Vab instead. Since ammeters have low resistance, under ideal conditions, would the voltage measure 0?

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  • $\begingroup$ "But what if you put an ammeter in to find Vab instead." What do you mean by "put an ammeter in". In where? Be specific. $\endgroup$ – Bob D Oct 18 '19 at 21:38
  • $\begingroup$ In series with R5 $\endgroup$ – Melanie Oct 18 '19 at 22:18
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Suppose you put a voltmeter to measure Vab which is the voltage from node Va to node Vb. This would just be the voltage in the branch: 5 * .064, if im not mistaken.

Not sure what 5 * .064 means. I think you mean the voltmeter would measure the voltage $V_{ab}$. If that's the case, yes it would.

But what if you put an ammeter in to find $V_{ab}$ instead. Since ammeters have low resistance, under ideal conditions, would the voltage measure 0?

Based on your clarification that the ammeter is put in series with $R_5$, yes it could be used to determine the voltage $V_{ab}$, provided that the input impedance of the ammeter is much less than $R_5$, just like the input impedance of a voltmeter placed between a and b would have to be much greater than the equivalent impedance between node a and b. But the ammeter would give you the current in $R_5$, which would not be a value of 0 volts, unless $V_{ab}=0$. It would measure a current equal to

$$I=\frac{V_{ab}}{R_5}$$.

From which you can calculate the voltage $V_{ab}$ as

$$V_{ab}=IR_{5}$$

Where $I$ = the ammeter reading.

Hope this helps.

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