Electrical Black Box Analysis - Data Plotting and Linear Regression · RMPH 2014 #1
Physics · electromagnetism
Problem
This experimental problem proposes an analysis for an electrical black box, which has three terminals - denoted by 1,2,3. To discover the elements that compose it, it is provided a measuring device comprising a voltage source variable (denoted by S), connected in series with an ammeter (denoted by A); the two terminals of the device are denoted by P and Q. To the same terminals P and Q is mounted a voltmeter (denoted by V). Ammeter and power supply have negligible internal resistance; internal resistance of the voltmeter can be considered as being infinite.
The terminals 1, 2 and P are placed in electrical contact. If terminals 3 and Q are also in electrical contact and the tension furnished by the source varies, pairs of values (indicated by the measuring instruments) are obtained. These data are given in the table 1. Current intensity is positive when the current passes through the ammeter from P to Q.
Table 1
| U(V) | -6 | -4 | -2 | 0 | 2 | 4 |
| I(A) | -0.2 | 1.2 | 2.6 | 4.0 | 5.4 | 6.8 |
Then, terminals 2, 3, P are putted in electrical contact. If and terminals 1, Q are also in electrical contact, the pairs of values indicated by the measuring instruments - where the voltage supplied by the source varies - are given in table 2.
Table 2
| U(V) | 0 | 2 | 4 | 6 | 8 | 10 |
| I(A) | -5.2 | -4.0 | -2.8 | -1.6 | -0.4 | +0.8 |
Finally, terminals 3, 1, P are putted in electrical contact. If terminals 2, Q are also in electrical contact, the pairs of values indicated by the measuring instruments - where the voltage supplied by the source varies - are given in table 3.
Table 3
| U(V) | -6 | -4 | -2 | 0 | 2 |
| I(A) | -0.6 | 0 | 0.6 | 1.2 | 1.8 |
Assume that all current-voltage dependencies are linear. In this problem, calculation of errors is NOT requested.
Task 1
1.a. Plot current - voltage dependence for the data set in Table 1.
1.b. Determine the numerical values of the intersections with coordinate axes of the graph. Determine also the slope of graph outlined in task 1.a. If applicable, write the result as a fraction.
1.c. Plot current - voltage dependence for the data set in Table 2.
1.d. Determine the numerical values of the intersections with coordinate axes of the graph. Determine also the slope of graph outlined in task 1.a. If applicable, write the result as a fraction.
1.e. Plot current - voltage dependence for the data set in Table 3.
1.f. Determine the numerical values of the intersections with coordinate axes of the graph outlined in task 1.e. Determine also the slope of graph outlined in task 1.e. If applicable, write the result as a fraction.