PAG 2.1 Determining Young Modulus Flashcards
Define Young’s Modulus
The Young’s Modulus of a material is it’s ratio of tensile stress to tensile strain. It is a measure of a material’s stiffness
How is stress calculated?
Stress= Force/ Cross-Sectional Area
How is strain calculated?
Strain = Change in Length/ Original Length
What is the unit of stress?
Pascals (Pa) or Nm^-2
What is the unit of strain?
Strain doesn’t have a unit since it is a ratio of two lengths
What is the unit of Young’s Modulus?
Pascals (Pa) or Nm^-2
How can the cross-sectional area of a thin wire be measured?
The wire’s diameter should be measured in several places along the wire, using a micrometer. The average diameter can then be used to calculate the circular area.
What safety precaution should be taken when stretching thin wires?
Safety goggles should be worn since the wire ,at snap when under a tensile load and this could cause eye injury.
Why should the temperature of the surroundings be kept constant when carrying out this experiment?
Metals undergo thermal expansion when there is a temperature increase, and this would change the dimensions of the wire
Why should a pre-stress be applied to the wire when setting up this experiment?
So that all the kinks in the wire are removed and the wire is taught, before measurements are taken
How can the Young’s Modulus be determined from a graph of extension against load?
The gradient of the graph is e/F
E=L/(A x gradient)
How can Young’s Modulus be obtained from a stress-strain graph?
The gradient will give Young’s Modulus
Suggest what has happened if the length of the wire doesn’t return to its original length when unloaded
The load may have exceeded the wire’s elastic limit and consequently the wire has undergone plastic deformation
How can the load applied on a wire be calculated from the mass added to the end of the wire?
Load = Mass x Gravitational Field Strength
F=mg
What safety precaution should be taken when using hanging masses?
Never stand with your feet below the hanging masses in case he wire snaps and the massses fall.
It is good practice to place a padded bucket below them
Suggest how the extension of the wire may be measured
A marker such as a small piece of tape could be added to the wire
A ruler could then be placed underneath the wire, allowing the movement of the marker 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, the wire may begin to deform plastically before a good range of results have been obtained
Suggest why a comparison test wire is used when conducting this experiment using Searle’s apparatus
So that any changes in the environmental conditions, such as a change in temperature, are accounted for and won’t skew the results obtained
Why is your choice of wire length important in this experiment?
Extension depends on length since
x=FL/AE
This means the length needs to be sufficiently long enough for the extensions to be easily measurable
Suggest how the wire may be fixed in lace when carrying out this experiment
Wire can be claimed tightly between two blocks of wood at one end. These blocks can then be claimed to the bench
Alongside a metre ruler, what other tool will help you measure the extension accurately?
A set-square can be used to help read the extension accurately
When measuring the diameter of the wire in multiple places, why should you rotate the wire between measurements?
Measure the wire in different orientations to ensure that the wire is circular across the full-length of the wire
How can the percentage difference in your experimental value and accepted value be calculated?
(Your value- Accepted value)/ Accepted value x 100
