Calculating the voltage over a resistance with and without voltmetre

In summary, the conversation involves a question about calculating the voltage of a resistance with and without a voltmeter. The initial attempt at a solution involves interpreting the ammeter as a current source and the voltmeter as a voltage source. However, the numbers provided do not follow Ohm's law and the diagram is incorrect. The conversation ends with a request for clarification on the problem statement.
  • #1
OldSnake
2
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?
 

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  • #2
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.
 
  • #3
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??
 
  • #4
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
 
  • #5
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...
 

FAQ: Calculating the voltage over a resistance with and without voltmetre

1. How do I calculate the voltage over a resistance?

To calculate the voltage over a resistance, you would use the formula V=IR, where V represents voltage, I represents current, and R represents resistance. This formula is known as Ohm's Law and can be used to calculate the voltage of a circuit with a known resistance and current.

2. What is a voltmetre and how does it work?

A voltmetre is an instrument used to measure voltage in a circuit. It consists of a meter with a scale that displays the measured voltage. To use a voltmetre, you would connect the positive lead to the point in the circuit where you want to measure the voltage and the negative lead to the negative terminal of the power source. The meter then measures the voltage by detecting the difference in potential between the leads.

3. Can I calculate the voltage of a circuit without a voltmetre?

Yes, you can calculate the voltage of a circuit without a voltmetre by using Ohm's Law and measuring the current and resistance with other instruments. However, using a voltmetre is the most accurate way to measure voltage in a circuit.

4. How does the voltage change when a resistance is added to a circuit?

When a resistance is added to a circuit, the voltage will decrease. This is because adding a resistance increases the overall resistance in the circuit, causing a decrease in current flow. According to Ohm's Law, with a decrease in current, there will also be a decrease in voltage.

5. Is it possible to measure the voltage of a circuit at multiple points?

Yes, it is possible to measure the voltage of a circuit at multiple points by using a voltmetre. You would simply connect the positive lead of the voltmetre to the desired point and the negative lead to the negative terminal of the power source. The voltmetre will then display the voltage at that specific point in the circuit.

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