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internal resistance of a battery planning

Extracts from this document...

Introduction

Physics coursework

Investigation to compare the internal resistance’s of different cells.

My task is to compare the internal resistances of different cells.  I will first make a prediction what I think the relation may be.  Then I will carry out preliminary and final experiments. After this I will then evaluate and analyse all of my results.  

Internal resistance is:

“The resistance within a voltage source, such as an electric cell or generator.” (http://www.answers.com/topic/internal-resistance-electricity)

EMF (electromotive force)

“The energy per unit charge that is converted reversibly from chemical, mechanical, or other forms of energy into electrical energy in a battery or dynamo.” (http://www.answers.com/topic/electromotive-force)

No real devices (batteries, amplifiers, generators) are perfect and so all have an internal resistance.  The resistance is caused because the charge has to flow through the cell.  When it does

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Middle

I set up the experiment as below.  Then I put different cell in and changed the resistance on the rheostat and recorded the results.  

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Conclusion

9

3.27

2.01

9

2.46

0.77

1.5

1.6

0.13

1.5

1.59

0.17

1.5

1.58

0.2

1.5

1.57

0.22

1.5

1.56

0.25

1.5

1.54

0.29

1.5

1.5

0.39

1.5

1.47

0.47

1.5

1.43

0.58

1.5

1.38

0.69

1.5

1.07

1.75

1.5

0.46

3.75

When doing my preliminary experiment I discovered that it would be better to use digital voltmeters and ammeters rather than one I used as it would be more accurate to use a digital ammeter and voltmeter.  This ensures there will be no errors when reading the values.   In my real experiment will also take repeats and also I will use more cells.  

The Real Experiment Method

I will set up the experiment as below.  I will implement different cells and change the resistance to get at least 8 readings for each cell.  I will wait for the equipment to cool down between each reading.  I will also use the same equipment throughout to attempt to stop any anomalies occurring.  

Safety

The experiment is very safe and so all I need to do is ensure the batteries do not get hot and that they do not leak as the contain very harmful and corrosive chemicals.  

...read more.

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