PAG 2.1 Determining Young Modulus

Question 1

Define Young’s Modulus

Answer 1

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

Question 2

How is stress calculated?

Answer 2

Stress= Force/ Cross-Sectional Area

Question 3

How is strain calculated?

Answer 3

Strain = Change in Length/ Original Length

Question 4

What is the unit of stress?

Answer 4

Pascals (Pa) or Nm^-2

Question 5

What is the unit of strain?

Answer 5

Strain doesn’t have a unit since it is a ratio of two lengths

Question 6

What is the unit of Young’s Modulus?

Answer 6

Pascals (Pa) or Nm^-2

Question 7

How can the cross-sectional area of a thin wire be measured?

Answer 7

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.

Question 8

What safety precaution should be taken when stretching thin wires?

Answer 8

Safety goggles should be worn since the wire ,at snap when under a tensile load and this could cause eye injury.

Question 9

Why should the temperature of the surroundings be kept constant when carrying out this experiment?

Answer 9

Metals undergo thermal expansion when there is a temperature increase, and this would change the dimensions of the wire

Question 10

Why should a pre-stress be applied to the wire when setting up this experiment?

Answer 10

So that all the kinks in the wire are removed and the wire is taught, before measurements are taken

Question 11

How can the Young’s Modulus be determined from a graph of extension against load?

Answer 11

The gradient of the graph is e/F
E=L/(A x gradient)

Question 12

How can Young’s Modulus be obtained from a stress-strain graph?

Answer 12

The gradient will give Young’s Modulus

Question 13

Suggest what has happened if the length of the wire doesn’t return to its original length when unloaded

Answer 13

The load may have exceeded the wire’s elastic limit and consequently the wire has undergone plastic deformation

Question 14

How can the load applied on a wire be calculated from the mass added to the end of the wire?

Answer 14

Load = Mass x Gravitational Field Strength
F=mg

Question 15

What safety precaution should be taken when using hanging masses?

Answer 15

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

Question 16

Suggest how the extension of the wire may be measured

Answer 16

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

Question 17

Why is the choice of wire diameter important in obtaining successful results?

Answer 17

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

Question 18

Suggest why a comparison test wire is used when conducting this experiment using Searle’s apparatus

Answer 18

So that any changes in the environmental conditions, such as a change in temperature, are accounted for and won’t skew the results obtained

Question 19

Why is your choice of wire length important in this experiment?

Answer 19

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

Question 20

Suggest how the wire may be fixed in lace when carrying out this experiment

Answer 20

Wire can be claimed tightly between two blocks of wood at one end. These blocks can then be claimed to the bench

Question 21

Alongside a metre ruler, what other tool will help you measure the extension accurately?

Answer 21

A set-square can be used to help read the extension accurately

Question 22

When measuring the diameter of the wire in multiple places, why should you rotate the wire between measurements?

Answer 22

Measure the wire in different orientations to ensure that the wire is circular across the full-length of the wire

Question 23

How can the percentage difference in your experimental value and accepted value be calculated?

Answer 23

(Your value- Accepted value)/ Accepted value x 100