Calculating the voltage over a resistance with and without voltmetre

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Homework Help Overview

The discussion revolves around calculating the voltage across resistors in a circuit involving a voltmeter and an ammeter. The problem includes two resistors of equal resistance and measurements of current and voltage, raising questions about the correct interpretation of the circuit setup and the application of Ohm's law.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants explore the implications of the given measurements and circuit configuration, questioning how to calculate voltage with and without the voltmeter. There is uncertainty about whether to combine resistances and how the presence of the voltmeter affects the readings.

Discussion Status

Some participants have suggested interpretations of the circuit, while others have pointed out potential misunderstandings regarding the placement of the ammeter and voltmeter. There is a lack of consensus on the validity of the original poster's drawing and calculations, with calls for clarification on the problem statement.

Contextual Notes

Participants note that the original poster's drawing may not adhere to Ohm's law, and there is confusion about the circuit configuration, particularly regarding the series and parallel relationships of the components involved.

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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