# Having to get as accurate measurements for resistance

Having the apparatus set up as pictured above (waszzzzzzzzoooooo), we will use the wire jockey to make contact with the Constantan wire between 0cm and 100ch at 10 cm intervals. With this connection we will note down both the current (amps) and potential difference (volts) with these we can work out the resistance (ohms) by using the formula R=V/I. We then repeat our experiment 4 times and find an average for the sake of accuracy. I plan to carry out the experiment under safe, controlled conditions in order to reduce the number of problems that could arise. However, some problems still remain such as the sharp wire, which could get hot.

If someone were to touch it they could easily cut or burn themselves. The way around this problem is to break the circuit when it is not in use. This also important because if the batteries were left in circuit their voltage would wear down reducing the accuracy of the results. Providing that common sense is used (i. e. not trimming eye lashes with hot wire) then there is very little that could go wrong. If, hypothetically someone was to trim their eye lashes with hot wire and stabbed their eye whilst doing so, then we would immediately stop the experiment and get them to the medical room.

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As previously stated the objective of this experiment is find relationships between the resistance and length of wire. In order to achieve this we have to get as accurate measurements for resistance as possible. This means we should try and eliminate or reduce any variable (with the exception of the one we are working on), which will dramatically influence the results. Possible variables, which cannot be completely eliminated, include: Length of constantan wire: This is the variable that we are working on. It is important that we make the connection as close to the distance we are testing as we can.

This means that a connector with a smaller surface area will be better i. e. the wire jockey, which has a smaller surface area than the crocodile therefore it can be placed directly on the interval. Temperature of wires: It is critical that we try to keep the temperature of the wires the same because the heating effect caused by the currant will raise the resistance of the wire. This happens because when a substance is heated its atoms gain energy and begin to vibrate. This makes it harder for electrons to flow increasing resistance.

Which in turn generates more heat. The only way to prevent it from heating is to remove the flow of electrons by breaking the circuit Power of the batteries: The voltage will wear down when in use, which will affect the resistance if R=V/I so we must break the circuit when it is not in use to reduce this effect. Connecting wires and other components on the circuit: These have their own resistances. In order to keep them from spoiling results we should make sure that we try to use the same ones. This means that we try and find the same ammeter and voltmeter etc.

But in a box of 20 of them this isn’t very easy. Prediction: I believe that by increasing the length of live constantan wire you will increase the resistance. I believe this because the constantan is what’s responsible for causing the resistance by slowing the electrons progress. As noted the atoms in the Constantan slow the electrons down causing resistance. Therefore if you were to double the amount of constantan it would, in theory double the resistance. However, in practice this may not be true as the constantan isn’t the only substance to offer resistance on the circuit.

The wires that run between the ammeters etc also bear their own resistance and as I don’t know what those wires are made from I can’t work out their exact resistance but I did take a measurement for 0cm of constantan, which should show roughly what those wires resistances were. E. g. say the resistance in the constantan at 10cm is 3ohms but over the whole circuit its 4 ohms. This means that the circuits connecting wires are responsible for 1 ohm of that. Now if we double the length of constantan to 20cm that should give 6 ohms but the length of the connecting wires hasn’t changed so it still gives 1 ohm.

The total resistance at 10cm is 4 ohms but the total resistance at 20cm is 6+1=7 and that isn’t double 4. It is however, constantly 1 ohm higher of what it should be. So without taking into account the resistance of the connecting wires the relationship between the length of the constantan and its resistance will progress in a linier fashion but with the connecting wires the relationship becomes stays linear but the resistance will be higher. Observations The first two tests were done using an ammeter, a voltmeter and 24swc constantan.