Physics - Module 5 - Materials/ Youngs Modulus

Question 1

Experiment to find the Young Modulus

Answer 1

Control wire - kept haut by the fixed force applied by the weight below
Length of wire to be tested (needs to be about 2m in length (diagram is not to scale)
Reference scale fixed to a
control wire
Vernier scale to measure extension and therefore the strain
Weight to keep the control wire taut
Mass hanger to vary the force applied and therefore vary the stress put on the load

Question 2

Young modulus

Answer 2

the ratio of stress to strain measured in Pascal (Pa)

Question 3

Tensile strain

Answer 3

the extension per unit original length

Question 4

Tensile stress

Answer 4

the force per unit cross-sectional area

Question 5

Area under force extension graph

Answer 5

Area under graph = work done = 1/2 x Force × Extension = 1/2Fx
Remember Hooke’s law : F = kx where k is spring constant

Work done = 1/2kx^2 = Elastic Potential Energy stored in spring

Question 6

Parallel spring

Answer 6

Two identical springs in parallel have a spring constant that is double the single spring constant.

Question 7

Series spring

Answer 7

Two identical springs in series have a spring constant that is half of the single spring constant.

Question 8

Experimental method for Hooke’s law

Answer 8

Measure the natural length of the spring (when no load is applied) with a mm ruler clamped to the stand. Make sure you take the reading at eye level and add a fiducial marker to the bottom of the spring to make the reading more accurate.
Add a weight to the spring. When it is at rest, record the new length of the spring. The extension is the change in length. You will also need to measure the mass using an electronic balance in order to calculate mg.
Repeat this process until you have at least 6 measurements.
• Plot a force extension graph. Draw a line of best fit. The gradient of the linear section of your graph is the force constant k.

Question 9

Extension

Answer 9

Extension = Extended length – Original length

Question 10

Gradient of force extension graph

Answer 10

The force extension graph is a straight line through the origin. The gradient of the graph represents the spring constant. Large gradient means a large spring constant ie a spring that is difficult to deform.

Question 11

Elastic limit

Answer 11

The limit the spring can stretch before it deforms.

Question 12

Hooke’s Law

Answer 12

Force is directly proportional to extension below the elastic limit.

Question 13

Compression

Answer 13

Forces shorten the length

Question 14

Tension

Answer 14

Forces that extend the length