Electromotive Force

Final Report

Introduction and theory

All sources of e.m.f. (Electromotive Force) have internal resistance r. For a power supply, this may be due to the wires and components inside, whereas for a cell the internal resistance is due to the chemicals within it. When this cell is connected to an external resistor of resistance R, the terminal p.d. (Potential Difference) across the cell is：

p.d. = e.m.f – Ir

where Ir is referred to as the lost volts of the internal resistance. Therefore, the smaller the internal resistance is, the larger the terminal p.d. is supplied with the current of the same size.

 Procedure

I connect the circuit well, the switch is in a disconnected state, and the slide rheostat is adjusted to the maximum.Then check whether the meter pointer is zero and the range is appropriate.

After the preparation, I first connected a battery as a power supply, adjusted the position of slide rheostat slide, read the meter reading of the meter and repeated 5 times and recorded it.Select three different batteries and repeat.Then I connected the three batteries in series and parallel, also adjusted the position of slide rheostat slide, read the voltage of the ammeter, and repeated 5 times.[pic 1]

I took all the experimental data and recorded them in a form, and then drew the U-I image after the experiment.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               Results

Table 1

Table 2

Analysis

Table 1