Is the Internal Resistance of the Voltmeter Accurate in Series Circuit?

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Homework Help Overview

The discussion revolves around a series circuit containing a 600 Ω and a 400 Ω resistor supplied by 90 V, with a voltmeter connected across the 600 Ω resistor. The original poster questions the accuracy of the voltmeter reading, which shows 60 V, and seeks to understand the internal resistance of the voltmeter.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to reconcile the voltmeter reading with theoretical expectations, questioning how a reading of 60 V can be accurate given their calculations. They explore the idea of using parallel resistance formulas to find the internal resistance of the voltmeter but encounter discrepancies with the expected result.
  • Some participants question the validity of the voltmeter reading and the assumptions made regarding its internal resistance, suggesting that a reading of 60 V may not be feasible.
  • Further inquiries are made about the absence of methods in the textbook for calculating the voltmeter's resistance, indicating a desire for clarification on the topic.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of the voltmeter's readings and the implications of its internal resistance. Some guidance has been offered regarding the need for a circuit diagram, indicating a potential direction for further exploration.

Contextual Notes

There is mention of a textbook reference that may not provide sufficient information on the topic, and the original poster expresses uncertainty about the accuracy of the book's claims regarding the voltmeter's resistance.

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Homework Statement


a resistor of 600 Ω and one of 400 Ω are connected in series and their combination is being supplied by 90 V. A voltmeter that is connected on edge of the resistor of 600 Ω shows 60 V. a) what's the internal resistance of the voltmeter.


The Attempt at a Solution



i found the real V in the resistor of 600 V which is 54 V. But the voltmeter shows 60 V. Now I don't know how is this possible

if they are in parallel could we just find the Rtot that will be Rv* Rs/(Rv+Rs) and then say I = V/R

and from this equation find the Rv? but i find false results using this method, the book says 3000 Ω
 
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The voltmeter reads 50 V if its internal resistance is 3000 ohm. 60 V is impossible.

ehild
 
ehild said:
The voltmeter reads 50 V if its internal resistance is 3000 ohm. 60 V is impossible.

ehild

hm, so the book has it wrong?

Im using the university physics by Hugh D. Young it's in chapter 27

never mind, let's suppose that it reads 50, how can I find the resistance of the voltmeter? There isn't any method inside the book, and our teacher never explained us anything like that, I'm just curious how this can be solved

thanks in advance
 
Draw the circuit diagram first. Show me, please.

ehild
 

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