User:Inconspicuum/Physics (A Level)/Material Structure Questions

Stress, Strain & Young's Modulus

1. 100N of force are exerted on a wire with cross-sectional area 0.50mm². How much stress is being exerted on the wire?
2. Another wire has a tensile strength of 70MPa, and breaks under 100N of force. What is the cross-sectional area of the wire just before breaking?
3. What is the strain on a Twix bar (original length 10cm) if it is now 12cm long?
4. What is this strain, expressed as a percentage?
5. 50N are applied to a wire with a radius of 1mm. The wire was 0.7m long, but is now 0.75m long. What is the Young's Modulus for the material the wire is made of?
6. Glass, a brittle material, fractures at a strain of 0.004 and a stress of 240 MPa. Sketch the stress-strain graph for glass.
7. (Extra nasty question which you won't ever get in an exam) What is the toughness of glass?
8. Wire has a tensile strength of 0.95Mpa, and breaks under 25N of force. what is the cross-sectional area of the wire before and after breaking?

Metals

1. Would you expect a metal to have more or less conductivity than a semiconductor? Why?
2. How can the stress-strain graph for a metal be explained in terms of ions in a sea of electrons?
3. As a metal heats up, what happens to its conductivity? Why?

Polymers

1. Different crystalline structures have different refractive indexes. Why does this mean that a polycrystalline polymer is translucent?
2. What sort of polymer is a pane of perspex?
3. What sort of polymer does the pane of perspex become when shattered (but still in one piece)?
4. What sort of polymer is a rubber on the end of a pencil?
5. What happens to the translucency of an amorphous polymer when it is put under stress?