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Internal Resistance

Extracts from this document...

Introduction

Group A

23 Feb 2009

Investigating the EMF and the internal resistance of a cell

The aim of this experiment is to find, investigate and analyse the nature of EMF in a circuit under variable resistances using different cells.

Internal Resistance is the force opposed to the flow of current inside a cell. It is caused by electronic and ionic resistances.

EMF (Electromotive Force) is :

“energy per unit electric charge that is imparted by an energy source, such as an electric generator or a battery”

http://www.britannica.com/EBchecked/topic/183352/electromotive-force

As we know all materials have resistance and no real cell is perfect. So our cell had also a resistance

that changes due to age and type of battery.

Middle

1.502

0.040

1.576

47

0.0331

1.519

0.033

1.580

56

0.028

1.583

68

0.0228

1.570

0.020

1.587

For Panasonic:

 Normal Old Resistor (Ohms) Current (Amper) Voltage (volts) Current (Ampere) Voltage (volts) 10 0.12 1.25 0.145 1.467 12 0.11 1.34 0.123 1.480 15 0.089 1.33 0.100 1.493 18 0.073 1.37 0.074 1.506 22 0.063 1.40 0.069 1.512 33 0.041 1.45 0.046 1.526 39 0.038 1.46 0.039 1.530 47 0.032 1.48 0.032 1.535 56 0.027 1.538 68 0.022 1.528 0.020 1.544

Conclusion

As the graph shows voltage and current are inversely proportional due to the negative slope of the best fit line. It means that P.D. (Potential difference) or Voltage produced by the resistor forces decreases when flows through the internal resistance thus thus causing voltage drop. Internal resistance reduces both the current and the voltage. The experiment showed us how the Voltage and Internal Resistance are connected by the V = E - Ir formula.

Bibliography:

Energizer  Dec 2005 Battery Internal Resistance [online] [accessed on 18 Feb 2009]

Available from World Wide Web:

http://data.energizer.com/PDFs/BatteryIR.pdf

Fitzpatrick R. Texas University Website14 July 2007 EMF and Internal Resistance [online] [accessed on 18 Feb 2009] Available from World Wide Web:

http://farside.ph.utexas.edu/teaching/316/lectures/node57.html

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