Calculating the voltage over a resistance with and without voltmetre

AI Thread Summary
The discussion centers on calculating voltage over resistances R1 and R2, both valued at 100 kilo ohms, with a current of 36.5 µA and a measured voltage of 0.4 V across a voltmeter. The original poster is confused about how to determine the voltage across the resistances without the voltmeter and questions the validity of their calculations, suggesting a voltage of 7.3 V without the voltmeter. Respondents criticize the drawing and calculations, stating they do not adhere to Ohm's law and emphasize that an ammeter should not be placed in series with a voltmeter. Clarification of the problem statement is requested to resolve the confusion regarding circuit configuration. The discussion highlights the importance of correctly applying Ohm's law in circuit analysis.
OldSnake
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Homework Statement



Here's a little drawing I made with all the info. In case my drawing is unclear. R1 is 100 kilo omhs
R2 is 100 kilo omhs as well. The current is 36,5 uA over the digital Ampere meter , And 0,4 Volt over the analog volt meter

Homework Equations



U= I x R
In a parallel currentflow U1=U2=U3
In a serieflow I1=I2=I3

The Attempt at a Solution



I'm completely baffled by this one. They're asking for the voltage of the resistance, but which one? Do they want me to add them together and are we even allowed to do that?
So R1+R2=R3 Which is 200k omh, but we still don't know the current over the resistance.
But we know the voltage over the voltage meter which is 0,4 Volt so the voltage over R3 is 0,4 V as well. Using I=U/R The current over R3 Is 0,000002 A. So the voltage of the resistance with voltmeter is 0,4 V, but how do you calculate it when you leave the voltmeter out of the picture?
 

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I think one way you can solve this is by interpreting the ammeter as a current source of that given value, and the 0.4V as a voltage source.
 
So the voltage over the resistance with voltmeter is 0,4 V and without 7,3 V (200k omhx36,5uA), but then the voltage over the resistance is larger than the battery??
 
Hey!

Your drawing doesn't make any sense. None of those numbers follow Ohms law and you would never insert an ammeter in series with a voltmeter like that.

What is the exact wording of the question?

Remember you can figure out any series or parallel circuit using Ohms law...

Voltage (V) = Current (I) x Resistance (R)

or

Current (I) = Voltage (V) / Resistance (R)

or

Resistance (R) = Voltage (V) / Current (I)


See what I mean? Following Ohms law, your numbers are meaningless...

AdeptRapier
 
AdeptRapier said:
Hey!

Your drawing doesn't make any sense. None of those numbers follow Ohms law and you would never insert an ammeter in series with a voltmeter like that.

I agree that the diagram is wrong. Could you please check the problem statement again and clarify? The only way they'd put an ammeter in series with the voltmeter in a circuit question like that, would be if the input resistance of the voltmeter were specified...
 
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