5 Determine the Young’s Modulus of a Material Flashcards
define Youngs modulus
ratio of tensile stress to tensile strain. its a measure of a materials stiffness
how is stress calculated
stress=force/cross-sectional area
what safety precautions should be taken when stretching thin wires
safety goggles should be worn since the wire may snap under tensile load which has potential to cause eye injury
how is strain calculated
strain=change in length/length
how can the cross sectional area of a thin wire be measured
the wires diameter should be measured at several different orientations at several different places along the wire, using a micrometer. the average average diameter can then be used to calculate the circular cross-sectional area
why should temperature of surroundings be kept constant when carrying out this experiment
metals undergo thermal expansion when temperature is increased, and contraction when decreased. temperature changes therefore lead to unwanted dimension changes of the wire
whybshould a pre-stress be applied to the wire at the beginning of the experiment
so that all the kinks are removed and the wire is taught, before any length measurements are taken.
how can Youngs modulus be determined from a graph of extension against load
gradient = extension/force
E=L/(A x gradient)
suggest what has happened if the length of wire does not return to its original length once load is removed
the wire may have exceeded its elastic limit and undergone plastic deformation
what safety precaution should be taken when using a hanging mass
never stand with your feet below the hanging mass incase the wire snaps and the mass falls.
how may the extension of the wire be measured
a marker such as a small piece of tape could be added to the wire. a ruler could then be placed under the wire allowing the movement of the tape to be measured
why is the choice of wire diameter important in obtaining successful results
if the wire is too thick the extension will be too small to measure. if the wire is too thin it may begin to deform plastically before a good amount of results have been obtained
suggest why a comparison test wire is used when carrying out this experiment whilst using Searles apparatus
so that any changes in the environment such as temperature are accounted for and won’t skew with the results
why is your choice of wire length important in this experiment
the length must be long enough so that the extension is easily measurable
along with meter ruler what other device could be used to help measure the extension accurately
a set square
