Method The wire is uncoiled from the roller carefully to make sure that there are no chinks in the wire. This would cause the wire to become weak at one point and would fracture before the wire could take its’ full strain. At one end of the wire, the wire is wrapped around a wooden block with another block laid on top. Then a g-clamp will tighten these blocks together trapping the wire, to prevent the wire from slipping. At the other end, there is roller pulley that simply allows weights to be added in the direction of the wire, using the weight hook and weights, attached by a strong knot.
A small piece of coloured cellotape will be attached to near both ends of the wire. As weights are added, there is a possibility that the wire may just slip rather than becoming taught and stretching. So, to take this into account, the celotape will have a scale underneath it and where the celotape is at first (from the wooden blocks or the roller pulley) the distance will be measured, and then as subsequent weights are added, the distance will be checked again to see if any slip has occurred, and then if slip has occurred, it will be taken into account and not added to the extension.
Procedure First several diameters of the Nicrome wire will be obtained, with a zeroing of the micrometer first, then obtaining an average. Note the micrometer will be cleaned first, in case any foreign particles interfere with the measuring of the Nicrome wire. The weights will be added in 100-gram increments, and then the marker at the wooden blocks will show if there is any slip, (It will be on top of a scale and if it’s moved from there slip has occurred). Then, the extension (minus any slip) will be obtained and tabulated.
This will be done by measuring the length of the wire from between the two markers, and then measuring the extension of the wire from the second marker. The weights will be added in 100 grams because this provides enough results without going in to small increments. The variable in this experiment will be the constant increment of force added to the wire. The expected force that the wire can support (based on preliminary work) will be up to and around 12 Newton’s’ which is when fracture occurred. Measurements to be taken.
The measurements to be taken at the start of the experiment will be the diameter of the wire (to calculate it’s cross sectional area), the original length of the wire without force added, the distanced from both markers to the ends (wooden blocks and the roller pulley). The measurements to be taken during the experiment are the length of the extension (a scale will be laid parallel to the vertical wire), which will take into accounts any slip that occurs. To check if any slip is occurring then the distances of the wire from the markers to the ends will be taken and then checked against the original distance.
This will be checked after every subsequent weight is added, and noted, to an accuracy of half a millimetre. Other measurements made will be the accuracy of the apparatus, such as the micrometer screw gauge must be zeroed before measuring the diameter, and the accuracy of the weights. Percentage error will be calculated in the evaluation. Safety Points The experiment is a safe experiment, but there is a chance of the weights dropping onto the experimenter’s foot, which can be avoided easily. The wire after fracturing may lash out to the other side of the bench.