Chapter 4: Testing Materials

Question 1

What type of a material is flint?

Answer 1

ceramic

Question 2

What type of a material is collagen?

Answer 2

polymer

Question 3

What type of a material is calcium phosphate?

Answer 3

ceramic

Question 4

What type of a material is bronze?

Answer 4

metal

Question 5

What type of a material is glass?

Answer 5

ceramic

Question 6

What type of a material is rubber?

Answer 6

polymer

Question 7

Give another example of a ceramic

Answer 7

china porcelain

Question 8

Give another example of a metal

Answer 8

iron

Question 9

Give another example of a polymer

Answer 9

polythene

Question 10

Give an example of a natural composite and a synthetic composite.

Answer 10

Natural - bone is made from the brittle ceramic calcium phosphate and the strong polymer collagen.
Man-made - carbon-fibre reinforced plastic is strong and lightweight.

Question 11

Would you expect a shelf loaded with books to be in tension or compression?

Answer 11

The upper surface will be in compression and the lower surface will be in tension.

Question 12

Name two brittle materials

Answer 12

glass, perspex, dried wood, china

Question 13

Name two tough materials

Answer 13

steel, fibreglass

Question 14

What is the equation for stress?

Answer 14

Stress = force/area

Question 15

What are the units of stress?

Answer 15

Pa or N/m^2

Question 16

What is the equation for strain?

Answer 16

Strain = extension/original length

Question 17

What is the elastic limit or yield point of a material?

Answer 17

The point at which a material begins to deform plastically.

Question 18

What is the breaking stress of a material?

Answer 18

The stress at which a material will break/fail.

Question 19

What is toughness?

Answer 19

How much energy is required to create new surface area in a material or how much energy a cubic meter of the material can absorb without cracks propagating.

Question 20

What is a brittle material?

Answer 20

The opposite of a tough material.

Question 21

What is yield stress

Answer 21

The stress at which a material begins to deform plastically.

Question 22

What is elastic deformation?

Answer 22

The temporary change in the shape of an object as a result of stress. Once the stress is removed, the object returns to its original shape.

Question 23

What is plastic deformation?

Answer 23

The permanent change in the shape of an object as a result of stress. Once the stress is removed, the object does not return to its original shape.

Question 24

Give an example of a ceramic with a very high yield stress

Answer 24

diamond

Question 25

What is the Young's Modulus?

Answer 25

A measure of how stiff a material is; namely the stress required for a particular strain.

Question 26

What is the equation for Young's Modulus?

Answer 26

E = σ/ε = FL/Ax

Question 27

What is brittle fracture?

Answer 27

When a material breaks/fractures after a certain stress is applied

Question 28

Which class of materials in generally the strongest?

Answer 28

ceramics

Question 29

Which are stronger, pure metals or alloys?

Answer 29

alloys

Question 30

How many times stronger is diamond than ice?

Answer 30

1000 times

Question 31

How much stronger is reinforced concrete than cement which has not been reinforced?

Answer 31

10 times

Question 32

A concrete block of cross-sectional area 0.01 square meters is crushed when a force of 1MN is applied to it. What is the breaking stress in MN/m^2? How many kg can the piece of concrete support?

Answer 32

breaking stress = 1/0.01=100MN/m^2 | maximum mass which can be withstood = 100000 kg.

Question 33

Are amorphous or crystalline materials more likely to be transparent?

Answer 33

amorphous materials.

Question 34

What metal ions make glass greenish in colour?

Answer 34

copper(ii)

Question 35

How do you calculate the refractive index of a material?

Answer 35

n=c/v=sin(i)/sin(r)

Question 36

Define the critical angle

Answer 36

The angle of incidence at which all of the ray is totally internally reflected.

Question 37

Pyrex has a refractive index of 1.47. For window glass, n = 1.51. In which does light travel faster?

Answer 37

Pyrex

Question 38

The refractive index of water is 1.33 (4/3). What is the speed of light in water (c=3x10^8 m/s)

Answer 38

v=c/n=2.25x10^8 m/s

Question 39

When does a refracted ray of light bend away from the normal?

Answer 39

When it enters a less optically dense material (with a lower refractive index)

Question 40

Equation for resistivity

Answer 40

ρ = RA/l

Question 41

Equation for conductivity

Answer 41

σ = Gl/A