Chapter 4

Question 0

Strong/strength

Answer 0

Strong: a large stress is needed to cause failure
Strength: the maximum stress a material can withstand before failure. Can have 2 values: one for yielding, one for breaking.

Question 1

Stress

Answer 1

Nm^-2/Pa. force applied divided by the cross sectional area it is applied to. We use the Greek letter sigma for stress. There are several types of stress e.g. Tension, compression, torsion.

Question 2

Weak

Answer 2

Opposite of strong

Question 3

Toughness

Answer 3

J/m^2. The energy required to create new surface area (J/m^2) or energy absorbed per unit volume (J/m^3). A tough material needs a large amount of energy to break it, undergoes a large amount of plastic deformation before breaking, resists crack propagation

Question 4

Brittle

Answer 4

Opposite of tough. Don’t undergo much plastic deformation, break soon after elastic limit. Crack easily and fracture suddenly. Brittle materials can be strong though!!!

Question 5

Hard

Answer 5

Pa. resistive to dents or scratches

Question 6

Elastic

Answer 6

Changes shape when a stress is applied but returns to its original shape when stress removed (without loss of energy)

Question 7

Plastic

Answer 7

Doesn’t return to its original shape after deformation. Plastic deformation is a permanent change of shape. Beyond elastic limit

Question 8

Ductile

Answer 8

Can easily be drawn into a wire

Question 9

Malleable

Answer 9

Can easily be hammered or pressed into a shape

Question 10

Filament lamp

Answer 10

Doesn’t obey ohms law, as when temp increases resistance increasing, allowing less current to pass with p.d.

Question 11

Strain

Answer 11

Change of length per unit length - a ratio

Question 12

Stress =

Answer 12

Force/area

Question 13

Strain =

Answer 13

extension/unstretched length - no units!

Question 14

Young modulus

Answer 14

Relationship between stress and strain. Measure of how stiff a material is - material property, not object

Question 15

Young modulus, E =

2

Answer 15

1) Stress/strain

2) force/area x length/extension

Question 16

Yield

Answer 16

A material suddenly ‘gives’ a little at the yield point. Material breaks/has reached elastic limit

Question 17

UTS

Answer 17

Ultimate tensile stress. Point where material is strongest. Unable to withstand stress beyond this point

Question 18

Breaking stress

Answer 18

Force per unit area. Dependant on object - not material property!

Question 19

Stiffness

Answer 19

How difficult it is to bend/stretch an object, e.g spring constant

Question 20

Resistivity

Answer 20

Constant - depends on material. Measured in ohms x metres

Question 21

Resistivity =

Answer 21

RA/L (resistance x area / length)

Question 22

Conductivity

Answer 22

Inversely proportional to resistivity. Measured in Siemens / metre

Question 23

Conductivity =

2

Answer 23

1) L/RA (length / (resistance x area))

2) conductance x length / area

Question 24

Area =

2

Answer 24

1) pi r^2

2) pi d^2 / 4

Question 25

Measuring resistivity

Answer 25

For different lengths of wire, find resistance, plot resistance on y axis, length on x axis; resistivity is gradient x area

Question 26

Energy stored in a spring =

2

Answer 26

1) 0.5•F•x (x is extension, F is force)
2) 0.5•k•x^2 (k is spring constant)
Area under graph for force against extension