A student is investigating how the extension e of an elastic cord depends on the diameter d of the cord when a force is applied. The student has a number of elastic cords of the same material with different diameters. The elastic cords have circular cross-sections. Each cord has an unstretched length of approximately 50 cm. It is suggested that the extension e and the cross-sectional area A of the cord are related by the expression E = FL / Ae where E is the Young modulus of the material of the cord, F is the force applied and L is the unstretched length of the cord. Design a laboratory experiment to test the relationship between e and d. Explain how your results could be used to determine a value for E. You should draw a diagram, on page 3, showing the arrangement of your equipment. In your account you should pay particular attention to • the procedure to be followed, • the measurements to be taken, • the control of variables, • the analysis of the data, • any safety precautions to be taken.