Electromotive Force and Internal Resistance of a cell

Internal resistance was rather different than from what we had first expected. Internal resistance was substantially lower than it should been. The total resistance of the circuit was not solely based on the variable resistance of the Rheostat itself but included its initial resistance. The Power Supply and the Rheostat (Variable Resistor) were the main sources of internal resistance. The Ammeter and Wires could only be accounted for marginal internal resistance. Yet 10.136 Volts is still too low a value to be correctly interpreted. For those reasons, it means that 1.864 Volts are missing somewhere in the circuit.

We were not able to get a theoretical literature value. There are three reasons for that. Firstly, even if we lower the resistance of the Rheostat, it will still have some resistance and hence we have to take this into consideration. Second reason is the thermal factor. When we increased the resistance of the Resistor, the current got lower and the Resistor got hotter. In other words, increasing resistance caused increasing temperature and then more increasing resistance. The last reason is that the clip bridging the main wire to the Resistor was not a good conductor. The clip that we attached to the Resistor was deemed to be another resistor rather than a conductor. These three factors affected our final value and hence it turned out that the EMF from our graph did not meet with the hypothetical value.

In order to get more accurate data, we first need to change the resistor in the Rheostat for another conductor such as plain wire. We should also have considered the thermal factor and should maintain constant temperature for the Resistor. There should be intervals between trials for cooling down. In addition, we need to use more conductive metal for the clip such as Aluminum or even Gold.