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
Messages
2
Reaction score
0

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?
 

Attachments

  • naamloos.JPG
    naamloos.JPG
    7.4 KB · Views: 491
Physics news on Phys.org
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...
 
Kindly see the attached pdf. My attempt to solve it, is in it. I'm wondering if my solution is right. My idea is this: At any point of time, the ball may be assumed to be at an incline which is at an angle of θ(kindly see both the pics in the pdf file). The value of θ will continuously change and so will the value of friction. I'm not able to figure out, why my solution is wrong, if it is wrong .
Thread 'Correct statement about a reservoir with an outlet pipe'
The answer to this question is statements (ii) and (iv) are correct. (i) This is FALSE because the speed of water in the tap is greater than speed at the water surface (ii) I don't even understand this statement. What does the "seal" part have to do with water flowing out? Won't the water still flow out through the tap until the tank is empty whether the reservoir is sealed or not? (iii) In my opinion, this statement would be correct. Increasing the gravitational potential energy of the...
Thread 'A bead-mass oscillatory system problem'
I can't figure out how to find the velocity of the particle at 37 degrees. Basically the bead moves with velocity towards right let's call it v1. The particle moves with some velocity v2. In frame of the bead, the particle is performing circular motion. So v of particle wrt bead would be perpendicular to the string. But how would I find the velocity of particle in ground frame? I tried using vectors to figure it out and the angle is coming out to be extremely long. One equation is by work...
Back
Top