OCR Physics A Level Determining Young Modulus: Module 1: Practical Skills in Physics. Questions with Complete Solutions

Define Young’s Modulus. The Young’s Modulus of a material its 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 N⋅m⁻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 N⋅m⁻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 may snap when under a tensile load and this could cause an 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? A pre-stress should be applied so that all 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 of a stress-strain graph will give you Young’s Modulus