Calculating Internal Resistance from Data: Exploring the Circuit

[Joshybosh]

This is my first post to the site.

Homework Statement

Theres a circuit with 6V battery, ammetre, switch, and variable resistor.
We are provided with primary data.
We use the equipment to find the current at to 2 different resistances
I have to decide what i want find out from my results. I decided to choose to find the total internal resistance.

Problem:
1| The Variable resistor had 3 dials on it and each went from 1-9.
Above the 1st 2nd and 3rd dial were the titles, "1A", "0.6A" and "0.3A"
Ive tried researching this but have come out clueless.

2| how do i find the anormalies and explain them and what can i find by comparing the sets of data.

Homework Equations

Equations i think i will find useful:

V=IRinternal
I=E x 1/(Rin+Rex)
V=E-IRinternal
P=I^2R
P=E^2 x 1/4R

value of R is +/- 0.2% at 18 oC
Here is a table of results, the first 4 rows were provided, and i had to find the rest.
R/W I1/A I2/A I3/A Mean I/A V1/V V2/V V3/V Mean V/V P1/W P2/W P3/W Mean P/W Range/V 1/2 Range Resolution Uncer % Uncert.
1.0 1.529 1.519 1.467 1.505 1.529 1.519 1.467 1.505 2.338 2.308 2.153 2.266 0.062 0.031 0.001 0.031 2.060
1.5 1.468 1.498 1.498 1.488 2.203 2.248 2.248 2.233 3.234 3.368 3.368 3.323 0.045 0.023 0.001 0.023 1.008
2.0 1.318 1.313 1.368 1.333 2.637 2.627 2.737 2.667 3.476 3.450 3.745 3.557 0.110 0.055 0.001 0.055 2.063
2.5 1.202 1.202 1.220 1.208 3.004 3.004 3.049 3.019 3.609 3.609 3.718 3.646 0.045 0.023 0.001 0.023 0.745
3.0 1.101 1.112 1.096 1.103 3.304 3.337 3.289 3.310 3.640 3.713 3.607 3.653 0.048 0.024 0.001 0.024 0.725
4.0 0.934 0.936 0.953 0.941 3.737 3.745 3.813 3.765 3.491 3.506 3.634 3.544 0.076 0.038 0.001 0.038 1.009
5.0 0.826 0.825 0.812 0.821 4.128 4.123 4.058 4.103 3.407 3.399 3.293 3.366 0.070 0.035 0.001 0.035 0.853
6.0 0.733 0.717 0.658 0.703 4.400 4.304 3.948 4.217 3.226 3.087 2.598 2.970 0.451 0.226 0.001 0.226 5.350
7.0 0.652 0.649 0.658 0.653 4.564 4.543 4.606 4.571 2.976 2.949 3.031 2.986 0.063 0.032 0.001 0.032 0.689
8.0 0.587 0.595 0.597 0.593 4.693 4.757 4.773 4.741 2.753 2.828 2.847 2.809 0.080 0.040 0.001 0.040 0.844
9.0 0.547 0.536 0.543 0.542 4.926 4.827 4.890 4.881 2.697 2.589 2.657 2.648 0.099 0.050 0.001 0.050 1.014
10.0 0.503 0.504 0.493 0.500 5.030 5.040 4.930 5.000 2.530 2.540 2.430 2.500 0.110 0.055 0.001 0.055 1.100
15.0 0.362 0.357 0.361 0.360 5.423 5.348 5.408 5.393 1.961 1.907 1.950 1.939 0.075 0.038 0.001 0.038 0.695

The Attempt at a Solution

1| I've been told that it might have something to do with limiting the current

2| I have made graphs from Current vs resistance, p.d vs power, p.d vs current. But am still unsure what i can find from these graphs. I think one of them can give you the internal resistance by finding the gradient.Any help would be great thanks, this has troubled so many people i know, so i thought i would ask people with a better knowledge of the subject.

 

[Mindscrape]

1) Yes, my guess would be that the dials represented the amount of power the variable resistor could handle, and simply divided by R and took the square root (P=I^2 R). Some resistances are made by coil windings, and maybe they didn't want you to put more than a certain amount of current into the windings. Maybe it doesn't mean anything, hard to tell without much context.

2) What is p.d.? Just compare your results from the experiment to the theoretical, ideal, results of the circuit.

Sorry about not being more help, but without a circuit diagram its hard to interpret. The table you made is kind of messy too, maybe put it into excel and post a screen shot of the excel table.

 

[Moetasim]

Hello, and thank you for your post. It seems like you are conducting an experiment to find the total internal resistance of a circuit using a variable resistor. From the data provided, it looks like you have measured the current and voltage at different resistances, and you want to use this data to find the internal resistance.

To start, you can use the equations you listed to calculate the values of the internal resistance for each set of data. Then, you can compare these values to see if there are any anomalies or inconsistencies. An anomaly could be a value that is significantly different from the others, or a trend that does not follow the expected pattern.

You can also plot graphs with the data you have collected to see if there are any trends or patterns. For example, you can plot a graph of current vs resistance and see if the data points follow a straight line. If they do, you can use the gradient of the line to calculate the internal resistance. If they do not, this could indicate an anomaly or some other factor affecting the results.

Another approach is to plot a graph of power vs resistance. This can help you see if there are any trends or patterns in the data that can help you calculate the internal resistance.

In terms of the anomalies you mentioned, it is possible that they are related to the dials on the variable resistor. It could be worth investigating if changing the settings on the dials affects the results in any way. This could provide some insight into the role of the variable resistor in the circuit and how it affects the internal resistance.

Overall, it seems like you have a good understanding of the equations and concepts involved in finding the internal resistance. I would suggest looking at the data and graphs you have collected and seeing if you can identify any patterns or anomalies that can help you calculate the internal resistance. Good luck with your experiment!