Outline plan: I will determine the extension of a piece of copper wire when various loads are placed upon it at the end. Using the results I will thus calculate Young`s modulus. Background Young modulus (E) is a quantity that describes the resistance of a wire to stretching. The quantity is a property of the specific material such as steel or copper. It gives the force per unit cross section of the wire required to produce a fractional change in length. The force per unit area applied to the wire is called the STRESS (or tensile stress), and the fractional change in length is called the STRAIN (or tensile strain).
Young’s Modulus is the ratio of the stress to the strain, that is: Young’s Modulus = stress/strain for the material I predict that a graph of extension against load will be a straight line through the origin, provided the elastic limit has not been reached, the gradient will give us L/ A E from which e can be calculated. Labelled diagram Consideration of safety: 1. Goggles must be worn at all times when a spring(s) are under tension in the room. This is because if the wire snaps etc. it could potentially hit you, and if in the eyes cause blindness, so its inperitive that they are worn at all times.
2. The “Loads” that are being used to extend the wire must have a cushion underneath their path on the floor to prevent damage to either the weight or the floor. Each participant must be aware of the weights and not place their feet or any other part of their body in the direct path of the mass 3. All bags and coats must be situated away from the working area so as to avoid tripping people up, and giving the maximum possible working space area. Apparatus list A2,4,6 Apparatus copper wire s. w. g.
Accuracy levels of equiptment Apparatus Accuracy/ + – mm Micrometer 0. 01 Scale 0. 1 Meter rule 1 Apparatus Accuracy/ + – kg-3 Scales 1 Detailed plan A wire suspended from a support is stretched by the weights hanging on the hanger. Notice that an initial 100 gram mass is attached. There are a number of measurements that you will need to take before the experiment is conducted.
– length (l) of the wire from its top support to the mass hanger – diameter (d) of the wire (use the digital micrometer), it is advisable to take this measurement in three separate places along the wire and twice at every position (rotating the wire 90 degrees to allow foe any oblongarities. – distance (L) Of the wire from the top support to the ruler beginning. o The experiment must be followed in a methodical step by step pattern so as to avoid easily made mistakes. o Firstly observing all the safety guidelines, set up the working area and the experiment apparatus as seen in the diagram.
o Before the experiment begins make sure that all the preliminary measurements have been taken and that the constants that you have identified will remain that way. o Firstly starting with your drawn “rough” results table fill ion the “starting” measurements. o These are done by using the meter rule to measure the length of the wire in accordance with the constant position of the sticky label on the wire. o Continue recording both the mass in grams and the final or new length on the table as you raise the load on the wire in increments of 50grams, ranging from the starting 100 grams to 600 grams.
o Do not exceed this weight as it begins to reach its elastic limit and the safety risk as identified earlier with the wire snapping could become apparent. o After the experiment is completed, tidy away all the equipment and remember not to take off the goggles until it is completely safe. o Now that all the results are written down they must be put in the correct units upon which they are needed in the formula ie. Changing of mass (Kg to weight (N) in this instant multiplying the mass by gravity. o I can now begin calculations and plot a force – extension graph.
Variables and constants The one variable in this experiment will be the load placed upon the wire, this is the obvious variable because as seen in the formula. By rearranging the formula to; e = F L A E We can see that there are 3 main factors which will effect the outcome of the experiment. The E symbolizes Young’s modulus, which will be effected by changes but is not itself a single factor as it is a measurement of the factors. In order for the experiment to be a success, it has to be a fair test.