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AS Physics > Chapter 4 materials > Flashcards

Chapter 4 materials Flashcards

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1
Q

What are ceramic materials?

A

Ceramic materials are hard and brittle this includes china and pottery, concrete and more.

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2
Q

What are polymers?

A

These are plastics such as polythene. Polymers are strong in tension.

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3
Q

What are composite materials?

A

Materials designed to combine the most desirable properties of two or more different materials.

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4
Q

How do engineers measure how easily a material fractures?

A

They measure measure how easily a material fractures be measuring the energy absorbed when a prepared specimen is broken.

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5
Q

What is the notch test?

A

1) Fix a sample to the testing machine.Raise the hammer(pendulum) to a pre-determined height.This gives it potential energy.
2) Let go of the swinging hammer.It breaks the bone.Some of the energy is used to break the bone.Note the height to which the hammer rises .This tells how much potential energy is left.The difference is the energy to break the bone.

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6
Q

Give an example of a polymer,ceramic and metal material.

A

Metal-Iron,steel,bronze,copper
Ceramic-Chine,clay,concrete,bone,glass
Polymer- Polythene,collagen,rubber,

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7
Q

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

A

1) Bone

2) Carbon-fibre reinforced plastic

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8
Q

Name two tough materials.

A

Steel and fibreglass.

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9
Q

What do compressive and tensile forces tend to do?

A

Compressive forces tend to squash an object.

Tensile forces tend to stretch it.

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10
Q

What classes of materials are there?

A

Ceramics,metal and polymers.

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11
Q

How are brittle materials different from tough materials?

A

Brittle materials break easily.

Tough materials require a lot of energy to break them.

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12
Q

Describe the properties of wood.

A

Wood is a natural composite material. It is composed of fibres of cellulose bound together by a substance called lignin.
-Cellulose fibres are stiff and strong,and the lignin prevents them from splitting apart.

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13
Q

Describe what the main foundations of a building should be like.

A

1) The foundations of a building must be able to support the weight of the building above so they must be strong in compression.
2) Horizontal sections of the building’s structure tend to bend under their own weight and because of the loads they have to bear.They are partly in compression and partly in tension,so a material must be chosen which is strong in tension and compression.

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14
Q

What material is often used for the foundations of buildings?

A

Concrete- Has a very high strength in compression, so it can support all the weight from the rest of the building.

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15
Q

What material is good for the horizontal sections of a building?

A

Timber is good for horizontal sections and so are metals like steel.Concrete and brick are less good because they are much weaker in tension than compression.

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16
Q

What is a problem with metals?

A

Metals “give” before they break. They reach a point where they permanently deform and start to bend and buckle.

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17
Q

What is the yield point?

A

The point at which a metal reaches its elastic limit and becomes permanently deformed. An architect must ensure that the metal does not reach this limit, if not it will bend or buckle.

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18
Q

What determines the useful strength of a metal?

A

The stress at the yield of point of a metal.

Breaking stress and yield stress are two ways of thinking about how strong a material is.

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19
Q

What is one pascal?

A

1 newton per square metre.

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20
Q

What is young modulus?

A

Measure how stretchy or stiff a material is.

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21
Q

What do polymers tend to be?

A

They tend to be elastic.

22
Q

What class of material is generally stronger?

A

Ceramics

23
Q

what is stronger, pure metal or alloys?

A

alloys

24
Q

A concrete block of cross-sectional area 0.01m^2 is crushed when a force of 1MN is applied to it.What is the breaking stress in MN m^-2? And in N mm^-2?How many kilograms can it support?

A

1) 100MN m^-2
2) 100N mm^-2
3) 100,000kg

25
Q

How much does 10N weigh on earth?

A

1Kg

26
Q

What is the strength of a material represented by?

A

Represented by its young modulus.

27
Q

What happens to materials after the elastic limit?

A

They either fracture or show plastic deformation.

28
Q

How do you work out young modulus?

A

Stress divided by strain.

29
Q

Explain how you can make white light coloured when putting it through coloured glass.

A

When light passes through coloured glass which absorbs specific wavelengths of light, the colour of the lights absorbed appear in the light on the other side of the glass.

30
Q

How do you get a spectrum when shinning light through glass.

A

Different coloured lights have different wavelengths and so are affected differently by refraction, different wavelengths bend more the shorter their wavelength which causes different coloured lights to split up forming a spectrum on the other side.

31
Q

What happens when light passes through glass?

A

Light slows down when it enters glass, and speeds up again as it leaves.The wavefronts are closer together in glass than air.

32
Q

How do you work out the refractive index of glass?

A

Speed of light in a vacuum /speed of light in glass.

33
Q

What is the speed of light in a vacuum?

A

3 x 10^8 m/s

34
Q

Why does glass go invisible when put in an oil of the same refractive index?

A

When two refractive indices match, the light doesnt change speeds as it passes from oil to glass.There is no reflection or refraction,so we cant see the glass.

35
Q

what is snell’s law?

A

sin i/sin r = refractive index.

36
Q

What happens light reaches a boundary between materials in which it travels at different speeds?

A

1) part is reflected

2) it bends as it enters the new material.

37
Q

Give two reasons why fibre optic systems have rapidly replaced copper wires for the transmission of electronic signals.

A

1) More information can be sent down a glass fibre than down a wire of the same thickness.
2) Signal can travel further without the need of amplification.

38
Q

What happens light reaches a boundary between materials in which it travels at different speeds?

A

1) part is reflected

2) it bends as it enters the new material.

39
Q

Give two reasons why fibre optic systems have rapidly replaced copper wires for the transmission of electronic signals.

A

1) More information can be sent down a glass fibre than down a wire of the same thickness.
2) Signal can travel further without the need of amplification.

40
Q

How does glass fibre optics work?

A

High purity glass is passed down a fine glass fibre,through reflection.

41
Q

Why does the intensity of light gradually decrease?

A

Light is absorbed by impurities or irregularities in the glass,using silica glass which is so pure that only one atom in a billion of impurity is present.

42
Q

what is exponential change?

A

Changing by the same factor for equal steps.

43
Q

What is the pattern in signal intensity?

A

The signal intensity is reduced by the same fraction every time the signal travels a given distance.

44
Q

With a torch under water when will the most light be reflected when the torch light is shined on the surface.

A

The greater the critical angle the more the light will be reflected.

45
Q

How do you work out the critical angle C?

A

sin 90/sin C= n so sin C= 1/n.

Btw Harris go to page 94 to 96 because there are diagrams you should know.

46
Q

What are smart materials?

A

Smart materials rely on fibre optics, fibres carry signals from sensors.

47
Q

Give examples of where smart materials are used.

A

1) An aircraft with a surface skin which can respond to changes in temperature,pressure,air speed and other atmospheric materials.
2) optics in bridges which can tell you the stresses of it main supports.

48
Q

What does the refractive index of a material determine?

A

It determines the angle through which the light is refracted.

49
Q

What shows how much light has slowed down?

A

The refractive index.

50
Q

No question

A

go over conductivity from the book.

AS Physics (6 decks)

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