4: Exam Questions

Question 1

Draw lines on force (y), extension (x) graph, with one (A) given

Answer 1

Same diameter. 2 x original length: 1/2 gradient of A

Question 2

Draw lines on force (y), extension (x) graph, with one (A) given

Answer 2

Same length, 2 x diameter: 4 x gradient of A

Question 3

Steel cables (on a crane) are strong, describe one other mechanical property that is important

Answer 3

stiff / high YM ; so does not stretch (too far under stress) /
tough / not brittle ; so does not break easily / cracks
don’t propagate / so does not snap easily

Question 4

Why would plastic make a better plug casing than ceramics?

Answer 4

plastics are tough(er) / not brittle / less brittle

Question 5

Define the term hardness

Answer 5

difficult to scratch / dent / wear away

Question 6

Define semiconductor

Answer 6

intermediate conductivity between metals and insulators / with a (much) lower density of charge carriers (than metals)

Question 7

Explain how the conductivity of a semiconducting material can be varied in the manufacturing process

Answer 7

by doping (with an element)
with more/less bonding electrons /
more/less free electrons / more doping raises conductivity

Question 8

Suggest 2 possible applications for graphene, one linked to mechanical properties and one to electrical properties
(Mechanical properties - strong, at one atom thick) (Electrical properties - conduction in one dimension) [4]

Answer 8

Mechanical e.g. cycle frames / car bodies / space/ elevator cable / carrier bags
car bodies strong for protection against impact / light weight
for fuel saving / strong and lightweight

electrical e.g. solar cells / transistors / circuits / LEDs / doped layers to make gates / touch screen

high strength / low density / high stiffness (directional) AND specified conductivity ( high / metallic / semiconducting / both / high charge carrier density)
e.g. touch screen conducting layers separated by insulators, which contact under pressure / electrical cables useful to minimise heat losses / weight / size