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# EMF and Internal Resistance of a cell

Extracts from this document...

Introduction

EMF and Internal Resistance of a cell

Data Collection

 Current (A) ± 0.005 Voltage (V) ± 0.05 0.42 0.70 0.38 1.00 0.28 1.40 0.18 1.75 0 2.35

Data Processing and Presentation

 Largest values of E and –r Smallest values

Middle

0.275

1.45

0.285

1.35

0.175

1.80

0.185

1.70

0

2.40

0.005

2.30

The equation E = V + Ir can be rearranged

E = V + Ir

V = E – Ir

V = –Ir + E

V = (–r) I + E

This allows us to plot V as y against I as x, in order to find the values of E and –r. Because the equation is now in the format y = mx + c, we know that E will be the y-intercept value, and –r will be the gradient.

I plotted three sets of data for current and voltage: my original results, the values including uncertainties that would give the largest values of E and –r, and the values including uncertainties that would give the smallest values of E and –r.

Conclusion

The variable resistor was not given time to cool down in between our recordings, so the temperature might’ve affected the results in some way. I only obtained five results, which might not have been enough for the experiment to really be considered accurate. Next time, I will record more paired values of the current and the voltage, as well as repeat the experiment at least once to reduce the chance of inaccuracy.

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