Physics Coursework Analysing Data - page 2
Keywords: Physics Report Analysising Data Extracting Information Calculation Potato Batteries
By Jenny on 02/07/2009
Level: A Level (Year 13)
Page Number: 2 of 5 pages: 1 2 3 4 5
0.76 + 0.34
Ecell = 1.10
So, the theoretical standard cell potential for the zinc-copper cell is 1.10 volts.
Diagram of the process taking place between zinc and copper electrodes in solutions of their salts
Results Table
External Resistance (Ω) Current 1(mA) Current 2 (mA) Current 3 (mA) Average Current (mA) Error in Current
(+/-) P.d.1 (V) P.d.2 (V) P.d.3 (V) Average P.d. (V) Error in P.d.
(+/-) log10 External Resistance Power
100 0.632 0.623 0.644 0.633 0.011 0.059 0.058 0.068 0.062 0.006 2.000 0.039
220 0.573 0.566 0.581 0.573 0.008 0.125 0.123 0.126 0.125 0.002 2.342 0.071
470 0.488 0.482 0.494 0.488 0.006 0.229 0.226 0.232 0.229 0.003 2.672 0.112
1000 0.340 0.336 0.343 0.340 0.004 0.419 0.414 0.422 0.418 0.004 3.000 0.142
2200 0.244 0.242 0.246 0.244 0.002 0.544 0.540 0.548 0.544 0.004 3.342 0.133
4700 0.147 0.146 0.148 0.147 0.001 0.676 0.671 0.679 0.675 0.004 3.672 0.099
10000 0.078 0.077 0.078 0.078 0.001 0.774 0.769 0.776 0.773 0.004 4.000 0.060
22000 0.038 0.038 0.038 0.038 0.001 0.833 0.828 0.834 0.832 0.004 4.342 0.032
47000 0.018 0.018 0.018 0.018 0.001 0.865 0.861 0.865 0.864 0.003 4.672 0.016
100000 0.008 0.008 0.008 0.008 0.001 0.881 0.877 0.882 0.880 0.003 5.000 0.007
220000 0.004 0.004 0.004 0.004 0.001 0.890 0.886 0.890 0.889 0.003 5.342 0.004
470000 0.002 0.002 0.002 0.002 0.001 0.894 0.890 0.895 0.893 0.003 5.672 0.002
1000000 0.001 0.001 0.001 0.001 0.001 0.893 0.893 0.897 0.894 0.003 6.000 0.001
2200000 0.000 0.000 0.000 0.000 0.001 0.898 0.894 0.899 0.897 0.003 6.342 0.000
The external resistance was the control variable which we varied. We took 3 readings each for the current and potential difference and used the averages, this minimises the affect of human error on our results.
Next I worked out the errors in these values by using the largest differences between the average and any of the values as the error. I have noticed that the error values decrease slightly as the resistances rises, particularly for the current.
My first graph is of potential difference against current.
I used the error values I worked out to draw the error bars on the graph.
The fact that all the points all fall in a fairly straight line indicates that the data is fairly accurate without any obvious anomalous results.
I can get quite a lot of information from this graph. I can use it to find out the emf and the internal resistance of the potato battery.
Electromotive force (emf) is the amount of energy given to a charge by a source of electrical energy – the potato battery.
Resistance is the opposition of a component to the flow of charge through it, internal resistance is simply the resistance inside the source of electrical energy.
(E = emf V = Voltage I = Current r = internal resistance)
Kirchoff’s 2nd Circuit Law
Sum of emfs = Sum of p.d.s
E = V + Ir →
This can be rearranged to give V = -Ir + E. If I am plotting current against voltage with current on the x axis and voltage on the y axis then that makes the gradient internal resistance and the y intercept emf.
I know that the equation for the best fit line of this graph is y = -1.335x + 0.8864.
So, r = 1335Ω (1.335 x 1000 because x axis values are in mA) and E = 0.8864V
As well as giving the equation of the graph Excel also gives its error (R2 = 0.9987) this means that it is 99.87% correct, so the error is 0.13%.
0.13% of 1335Ω = 1.7355
r = (1335 +/- 1.7355) Ω
To do the same thing without
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