Combined resistance of a cell and an ammeter

[fickle]

[SOLVED] Combined resistance of a cell and an ammeter

Homework Statement

I had to do a lab where a 105cm 28 swg wire was used to find the combined resistance of a cell and an ammeter. The only apparatus was a switch, 1.5v cell, 0-1A ammeter, 105cm & 20cm wires and connecting wires.

Switch, cell and ammeter are connected in series, and the 105cm wire is connected at the ends of the switch and ammeter. For 6 different lengths of the wire, the current readings are recorded. After that, the 20cm wire is inserted between the switch and the cell in the circuit, and the current readings are recorded for the same lengths of the 105cm once more.

Results:

For lengths increasing from 15cm to 90cm:

Current without 20cm in circuit/A:
0.36, 0.30, 0.26, 0.22, 0.20, 0.16

Resistance without 20cm in circuit/Ohms:
4.17, 5.00, 5.77, 6.82, 7.50, 9.38

Current with 20cm in circuit/A:
0.24, 0.22, 0.20, 0.18, 0.16, 0.12

Resistance with 20cm in circuit/Ohms:
6.25, 6.82, 7.50, 8.33, 9.38, 12.50

Homework Equations

Two graphs were plotted of the equation R = k(1/S) - r

Where R is the resistance of the length of the 105cm wire, k is a constant, S is the current reading and r is the resistance of the other components in the circuit, assuming the connecting wires have negligible resistance.

The Attempt at a Solution

Well, I've plotted both graphs of R against 1/S; finding R from V/I for the observations. k is the gradient, and it's the same value on both graphs, 1.5. It was advised to extend the y-axis (R) to -2 ohms. -r, the y intercept and the resistance of the cell and ammeter that I am supposed to find is zero on both graphs. Is this possible? Can it really be zero?

I'm wondering if my teacher set up the lab to give this value by changing the suggested wires to be used in the experiment, to test a skill we're supposed to be assessed by in our labs. I just want to know if it's realistic to get a dead zero y-intercept for a graph of this equation, or if I measured something incorrectly during the lab.

Any help would be appreciated! Thanks!

 

[Nate810]

[SOLVED]Yes, it is possible to get a y-intercept of zero with this equation. The value of r in this case is the sum of the resistances of the cell and ammeter, which can indeed be zero if their resistances are equal.

 

[ogb p]

Based on the data and equations provided, it is possible to get a y-intercept of zero for the graphs of R against 1/S. This would mean that the resistance of the cell and ammeter is negligible compared to the resistance of the 105cm wire. This could be due to the type of materials used in the construction of the cell and ammeter, as well as the quality of the connections between them and the wire. It is also possible that there were some errors in the measurements or calculations during the lab, so it would be beneficial to double check your work and possibly repeat the experiment to confirm the results. Overall, it is not uncommon to get a zero y-intercept in this type of experiment, but it is important to ensure the accuracy of the data and results.