Finding the emf and internal resistance of a cell

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SUMMARY

The discussion focuses on a method for determining the electromotive force (EMF) and internal resistance of a cell, specifically one with an approximate EMF of 1.5V and internal resistance of 1Ω. The proposed method involves using the equation ε=Ir+IR, rearranged to V=-Ir+ε, to create a linear graph where the y-intercept represents the EMF and the gradient indicates the internal resistance. The experiment entails adjusting a rheostat to obtain ten voltage and current readings without exceeding 1.5 amps, which is deemed a valid approach for this analysis.

PREREQUISITES
  • Understanding of Ohm's Law and circuit theory
  • Familiarity with linear graphing techniques
  • Knowledge of using ammeters and rheostats in experiments
  • Basic concepts of electromotive force (EMF) and internal resistance
NEXT STEPS
  • Research the use of linear regression for analyzing experimental data
  • Learn about the characteristics of different types of cells and their internal resistances
  • Explore advanced methods for measuring EMF and internal resistance, such as using an oscilloscope
  • Investigate the impact of temperature on the internal resistance of batteries
USEFUL FOR

Students in physics or electrical engineering, educators designing laboratory experiments, and anyone interested in practical applications of circuit theory and battery analysis.

dtwazere
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I hope someone can help me with my coursework by making sure my method is ok and is actually correct for my experiment. Note. I will not actually be doing this it is just a plan of what I could do!

1. I am provided with a cell of approcimate EMF 1.5V, an approximate internal resistance of 1Ω and an approximate energy capacity of 1.5Ah. I have to plan an experiement to find the EMF and internal resistance.



2. I know that i will be using the equation ε=Ir+IR and rearranging it to give V= -Ir +ε and linking it with the general equation for a linear graph y=mx+c. I know the y intercept will be the EMF and the gradient, -r, will be my internal resistance.



3. For my method i will be setting up my experiment like this:http://img232.imageshack.us/img232/774/experimentma5.th.jpg

I want to know if my method is correct. I will turn on the cell and adjust the rehostat until i find the lowest current recorded on my ammeter. I will then read off my voltage and make a table of both readings. I will then adjust the rheostat each time so I take 10 readings of voltage and current but i will not exceed 1.5 amps. Does this method seem ok? I am confused on whether it is correct or not.

Thanks in advance for your help,

Daniel

 
Last edited by a moderator:
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Seems pretty all right to me.
 

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