Physics Coursework Analysing Data - page 3
Keywords: Physics Report Analysising Data Extracting Information Calculation Potato Batteries
By Jenny on 02/07/2009
Level: A Level (Year 13)
Page Number: 3 of 5 pages: 1 2 3 4 5
Excel I drew two best fit lines which show the furthest out my values could be while still hitting the error bars.
I already know that the gradient is internal resistance and the y intercept is emf for these lines.
Line Internal Resistance (Ω)
Minimum 1250
Best fit 1335
Maximum 1444
The difference between the minimum value and the best fit line is 85Ω and the difference between the maximum value and the best fit line is 109Ω.
We use the biggest difference so the error is 109Ω.
r = (1335 +/- 109) Ω
Line Emf (V)
Minimum 0.8650
Best fit 0.8864
Maximum 0.8950
The difference between the minimum value and the best fit line is 0.0214V and the difference between the maximum value and the best fit line is 0.0086V.
We use the biggest difference so the error is 0.0214V.
E = (0.8864 +/- 0.0214)V
That’s all the information I could get from that graph.
Another value can get from my initial results is power, the equation P = VI
(P = Power).
Power is the rate of delivery of energy.
I decided to work out the values for power and for my next graph I plotted external resistance against power. Because the change in the external resistance is so large I had to plot it on a logarithmic scale to fit it on.
I can use my knowledge of the maximum power transfer theorem to extract information from this graph.
The maximum power transfer theorem states that the external resistance will affect the current drawn from a source of emf, and therefore the energy lost within it. It is possible to find the value of this external resistance R that will give the greatest power output. In the circuit below consider the variation of output power with R.
E = IR + Ir
EI = I2R + I2r *(EI = PR + Pr)
Therefore, d (I2R) / dR = E (dI / dR) 2Ir (dI / dR) = 0 for a maximum
(d = rate of change)
Therefore, E (dI / dR) = 2Ir (dI / dR) and so, E = 2Ir
This, therefore gives r = R for maximum power output.
For example, this is the case for an amplifier and a loud speaker; the output impedance of the amplifier should be matched to that of the speaker. This condition does not give the most efficient operation of the system however.
Basically when the source gives out its maximum power when external resistance is the same as the internal resistance
In the context of my graph this means that the value
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