As the title suggests, what I intend to do in this experiment is find out what factors will affect the resistance of a wire. For example, if the length of a wire is shortened, then will the resistance increase or decrease. Fair test: In order to make this experiment a fair test, to obtain reasonable results, only one thing can be changed. All the other factors/variables would have to remain exactly the same. For example, if the length of the wire were being decreased at a reasonable measurement range then that would be the only thing that should be changed.
The type and thickness and voltage should not changed, otherwise that could affect the results obtained. Safety As in every scientific experiment, safety precautions must be followed. The safety measures to be taken here are as follows: A heatproof mat must be placed underneath the wire, in case the wire gets too hot. Do not hold the wires with hands. Always use the crocodile clips, as the wire would most definitely burn your hands if it got too hot (especially when the wire is below 30 or 40 cm, as these are the measurements when the wire could overheat). Apparatus: Power pack.
5 connecting wires 2 crocodile clips Digital ammeter (gives more accurate results) Analogue voltmeter Heatproof mat Wires (different length, thickness and type) Diagram: Method: Set up the equipment as shown in the above diagram, making sure the heatproof mat is under the wire. Draw a rough table to record the results. Clip the crocodile clips to each end of the wire. Remember distance between them should be 1 meter. Switch on the power pack and take the readings from the digital ammeter, connected in series and analogue voltmeter, connected in parallel.
Remember to keep voltage the same throughout the experiment to make it a fair test. The power should be turn off while results are being recorded so that the wire does not overheat and burn. Decrease wire by 10cm. Repeat the previous steps until wire is only 10cm and you have 10 readings. You must have at least 6 readings so you can use them to plot a graph. Don’t worry if when you get to the measurements of 30cm or below, the readings seem a bit peculiar, as at that point the wire might overheat and jump off the readings. Make a neat copy of a results table and plot a graph, showing the line of best fit.
Prediction: I predict that as the length of the wire decreases, the resistance will decrease. Therefore as the wire length increases, the opposite will happen and the resistance will increase because the resistance has more atoms to collide with. The reason I predict this is because long wires have more friction, resistance is increased; the less the current will flow. If the thickness of the wire is changed, then I predict that the thicker the wire, then the resistance will decrease and the thinner the wire then the higher the resistance will be.
The reason being that thick wires have more space for the resistance to pass through; more current can flow through because it is a better conductor. Measurements: The ranges of measurements I will be using in this investigation are as follows: The length of the wire will be shortened every 10cm. The reason being that I can get enough readings to plot the graph and the results should be close enough to compare to one another. When I test the different thickness, I will be testing each of them at 1 meter. N. B: When the wire reaches a length or 30cm or below, the wire could overheat and jump off the readings, causing some peculiar results.
Ohm’s Law: The ohm’s law tells us that ‘The resistance of a wire is the same, whatever current is flowing through it, provided that the temperature remains constant. ‘ Ohm’s law was worked out by George Ohm, a German scientist, who said that Resistance = Voltage divided by current. So Ohm’s law gives us a way of working out the relationship between Voltage and current, and the concept of resistance. Ohm’s also showed the resistance on a current- voltage graph, to show how the current affects the voltage produced over a component. Usually the horizontal axis of the graph is the current and the vertical axis is the voltage.
For a particular current, you should be able to read what voltage should be produced. Also, if you know what voltage was applied to a component, it will tell you what current will pass through it. The gradient of a current- voltage graph can tell the resistance of the component. If the graph is a straight line, then the resistance is the same for any current. A straight line has a constant gradient. If the graph is curved, then the resistance changes depending on current is being used. If the gradient gets steeper, with more current, then the resistance has also increased.
(Reference- science encyclopaedia)
OBTAINING (Results) As the above results tables show, as the wire decreases in length the resistance decreases too and the longer the wire, the longer the wire, the lower the resistance. Therefore my prediction was correct. The reason the resistance is lower is because it has less space to move through when the wire is shortened. The resistance was calculated by dividing the voltage by the current. The table shows the various lengths of the same wire (34 constantan) and their resistance.
If observed carefully, you will find that there is not much difference between each one. The difference, ranges from 0. 5 to 1. 5. Therefore as you will see in the graph, the resistance is constant. In order to obtain accurate results, as a group, we used a digital ammeter to measure the current. The current is more or less constant, however when the wire reaches to the length of 30cm and below, the readings jump off the scale. This could be because the wire has overheated and therefore the peculiar readings. For example, when the length was 20cm the ammeter reading was 2.
6 A when the previous reading (30cm) was 1. 075. That is a huge jump compared to the differences between the other readings. Table three shows the results of the different thickness of wire. 26, which is the thickest wire has the lowest resistance and 32, which is the thinnest wire, has the highest resistance, just as my prediction suggests. The results do seem accurate, however at first I did think that the reading of the 32 constantan copper wire was a bit high. Then I remembered an important fact about copper. It is an extremely good conductor, which is why when experimenting the wire got hot very quickly.