How to Determine the EMF of a Battery Using Two Voltmeters?

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SUMMARY

The discussion focuses on determining the electromotive force (EMF) of a battery using two voltmeters with different readings. When connected individually, the voltmeters read V1 = 0.9V and V2 = 0.6V, while connected simultaneously, they read V3 = 0.45V. The equations derived from the readings include V1 = E - I1R1, V2 = E - I2R2, and V3 = E - I3R3, where I1, I2, and I3 are the currents through the respective voltmeters, and R1, R2, and RB are their resistances. The discussion emphasizes the importance of understanding the differences between ideal and real voltmeters and batteries in calculating the EMF accurately.

PREREQUISITES
  • Understanding of Ohm's Law and circuit analysis
  • Familiarity with the concepts of ideal and real voltmeters
  • Knowledge of electromotive force (EMF) and internal resistance of batteries
  • Ability to solve simultaneous equations in electrical circuits
NEXT STEPS
  • Study the principles of circuit analysis using Kirchhoff's laws
  • Learn about the characteristics of ideal vs. real voltage sources
  • Explore methods for measuring internal resistance of batteries
  • Practice solving simultaneous equations in electrical engineering contexts
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Students in electrical engineering, physics enthusiasts, and anyone interested in practical applications of circuit theory and battery analysis.

palkia
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Homework Statement


We have to measure emf of a battery. We have to voltmeters. Each of them when connected alone across the battery, they read V1 = 0.9V and V2 = 0.6V and when both of them are connected to the battery simultaneously, they both read V3 = 0.45V . What is the emf of battery

Homework Equations


E-ir=V

The Attempt at a Solution


I don't know how to proceed...I thought the voltage across the battery will be it's emf when connceted without a load but it is showing different readings for the voltmeter
 
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Find out the difference between an "ideal" voltmeter and a "real" voltmeter. Likewise ideal and real batteries.
 
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ideal voltmeter-Which doesn't influence the circuit

Real voltmeter-Which has resistance that is not infinitely largeSame for battery
 
okay so it makes sense that it shows different readings now...but still How can I proceed if they have different resistance
 
Ok so you will need to decide how many unknowns there are and give them names (eg R1 is the resistance of Voltmeter 1).

Then write some simultaneous equations and if you have enough then you can solve them.
 
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V1=E- I1R1
V2=E-I2R2
V3=E-I3R3

It's getting bigger to solve as I tried
 
In the last case,when we connect the voltmeters ,my book states that I3=I1+I2 but I am not sure How it came
 
palkia said:
V1=E- I1R1
V2=E-I2R2
V3=E-I3R3

I don't think those are correct. What about the battery resistance? With just one voltmeter connected the circuit looks like this...

Battery Circuit.jpg


So the equations would be

V1 = EMF - (I1*RB)
you also know
I1 = V1/R1

V2 = EMF - (I2*RB)
you also know
I2 = V2/R2

With both meters connected...

V3 = EMF - (I3*RB)
you also know
I3 = V3/R3
and
R3 = R1 in parallel with R2
 

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