In the experiment carried out we have used the following equipments:
Battery (or cell) – 1.5 V
Wires
Switch
Variable Resistors (10 items)
Voltmeter
Ammeter
Using equipments listed above the experiment circuit was set up as shown below:
By changing the resistors different values on Ammeter and Voltmeter were taken for all of them. The resistors were chosen between 0 ohms and 100 ohms. The values were measured three times each in order to check their reliability. Also age types of cell were used, as old cells were considered to be “weak”. The cells were used accurately so that they did not run out. Preferably electronic ammeter and voltmeter were advised as they show more correct values.
Values are then were used to build a graph* of y=mx+c which is V=E – Ir in this experiment to display the relationship between current and voltage. The y-axis was for voltage and x-axis for current. Then drawing best fit line helped to find the average EMF and internal resistance for the circuit and the cell. The internal resistance will be the gradient r (negative) and EMF will be th y-intercept.
*Graphs on a graph paper
RESULTS:
For Duracell:
For Panasonic:
For Long Life:
Analysis:
Using graph the values for EMF and r were obtained.
Also we can check them by substituting them into the formula
V = E – Ir
E is supposed to be smaller than V because of the changing resistors.
So r = V/I
Conclusion:
Finally it is necessary to admit that due to human errors in measuring inaccurate values might be taken for result. However, it is exactly what's expected because it is impossible to get a perfect line in graph with assuming all anomalies. All results were triple-checked and corrected.
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:
Fitzpatrick R. Texas University Website14 July 2007 EMF and Internal Resistance [online] [accessed on 18 Feb 2009] Available from World Wide Web:
