Determination of Young's Modulus

Question 1

What is the Unit of Stress

Answer 1

Pascals (Pa) or Nm^-2

Question 2

What is the unit of Strain

Answer 2

Strain is unitless since it is a ratio of two lengths

Question 3

What is the Unit of Young’s Modulus

Answer 3

Pascals (Pa) or Nm^-2

Question 4

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

Answer 4

• The wire’s diameter can be measured
• It should be measured in several places along the wire, using a micrometer
• The average diameter can then be used to calculate a mean cross sectional area

Question 5

What safety precaution should be taken when stretching thin wires

Answer 5

Safety googles should be worn since the wire may snap when under a tensile load and could cause an eye injury

Question 6

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

Answer 6

• Metals undergo thermal expansion when there is a temperature increase
• This would slightly change the dimensions of the wire

Question 7

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

Answer 7

A pre stress should be apllied so that all kinks in the wire are removed and the wire is taught before measurements are taken

Question 8

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

Answer 8

The gradient of the graph would be e / F

E = L / A x Gradient

Question 9

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

Answer 9

If 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

Question 10

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

Answer 10

Load = Mass x Gravitational Field Strength

F = mg

Question 11

What safety precaution should be taken when using hanging masses

Answer 11

• Never stand with your feet below the hanging masses in case the wire snaps and the masses fall
• It is good practise to place a padded bucket below them

Question 12

Suggest how the extension of the wire may be measured

Answer 12

• 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 13

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

Answer 13

• 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 14

Suggest why a comparison test wire is used when conducting this experiment

Answer 14

A comparison wire is included so that any changes in the enviromental conditions such as a change in temperature are accounted for and won’t skew the results obtained

Question 15

Why is your choice of wire length important in this experiement

Answer 15

• The extension of the wire depends on the wire’s length since
• Extension = FL / AE
• This means the length needs to be sufficiently long enough for the extensions to be easily measureable

Question 16

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

Answer 16

• The wire can be clamaped tightly between two blocks of wood at one end
• These blocks can then be clamped to the bench

Question 17

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

Answer 17

A set sqaure can be used to help read the extension accurately

Question 18

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

Answer 18

You should measure the wire in different orientations to ensure that the wire is circular across the full length of the wire