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

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SUMMARY

The discussion centers on calculating the internal resistance of a voltmeter connected in series with resistors of 600 Ω and 400 Ω supplied by 90 V. The voltmeter displays 60 V, which contradicts the expected voltage drop across the 600 Ω resistor, calculated to be 54 V. The correct internal resistance of the voltmeter is identified as 3000 Ω when it reads 50 V, highlighting a discrepancy in the voltmeter's reading that raises questions about the accuracy of the measurement.

PREREQUISITES
  • Understanding of Ohm's Law and voltage division in series circuits.
  • Familiarity with the concept of internal resistance in measuring instruments.
  • Basic circuit analysis skills, including series and parallel resistor calculations.
  • Knowledge of how to interpret voltmeter readings in electrical circuits.
NEXT STEPS
  • Research the principles of voltage division in series circuits.
  • Learn about the effects of internal resistance on measurement accuracy.
  • Study circuit analysis techniques for mixed resistor configurations.
  • Explore practical applications of voltmeters and their calibration methods.
USEFUL FOR

Students studying electrical engineering, physics enthusiasts, and anyone involved in circuit design and analysis who seeks to understand the implications of measurement accuracy in series circuits.

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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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