# Homework Help: Making sense of data

1. Mar 10, 2008

### Joshybosh

This is my first post to the site.

1. The problem statement, all variables and given/known data

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.

2. Relevant 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

3. The attempt at a solution
1| ive 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.

2. Mar 11, 2008

### 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.