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A level physics > Materials > Flashcards

Materials Flashcards

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1
Q

What is Hooke’s Law?

A

The extension is directly proportional to the force applied up to the limit of proportionality

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2
Q

What is the equation for Hooke’s law?

A

F=ke

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3
Q

What is density?

A

Density is a measure of the compactness of a substance

also defined as its mass per unit volume

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4
Q

What is the equation for density?

A

Density(kgm^-3) = mass(kg) / volume(m^3)

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5
Q

How can we find out which substance is denser as we compare two substances?

A

The substance with the greater mass in the same volume is denser than the other.

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6
Q

How can the density of a regular solid be measure?

A
  • measure its mass using a top-pan balance
  • measure the dimensions using vernier callipers and calculate its volume using the appropriate equation
  • calculate the density
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7
Q

How can the density of a liquid be measured?

A
  • measure the mass of an empty measuring cylinder
  • pour the liquid into the measuring cylinder and measure the volume directly
  • measure the mass of the cylinder and liquid to calculate the mass of the liquid
  • calculate the density
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8
Q

How can the density of an irregular solid be measured?

A
  • measure the mass of an object
  • Immerse the object in a liquid in a measuring cylinder or beaker and observe the increase in liquid level-this is the volume of the object
  • calculate the density
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9
Q

What is an alloy?

A

An alloy is a solid mixture of two or more metals.

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10
Q

How do you find out the volume of a cuboid?

A

volume = abc

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11
Q

How do you find out the volume of a cylinder?

A

volume = (pi*diameter^2 )/ 4 * height

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12
Q

What happens when a spring is stretched?

A

The stretched spring exerts a pull(tension) on the object holding each end of the spring

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13
Q

What is the elastic limit?

A

This is the maximum force that can be applied onto a material and still regain its original shape.

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14
Q

What is the standard form of measurement units from Giga to picto?

A 
G(billion)-1*10^9
M(million)-1*10^6
K(thousand)-1*10^3
cm-1*10^-2
mm-1*10^-3
µ(micro)-1*10^-6
n(nano)-1*10^-9
p(picto)-1*10^-12
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15
Q

What are tensile forces?

A

Stretching forces

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16
Q

What are compressive forces?

A

Squashing forces

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17
Q

What are shear forces?

A

Cutting forces which change the area of the object

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18
Q

What are torsional forces?

A

Twisting forces which change the area of the object

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19
Q

What happens to the extension when the springs are in parallel?

A

The extension halves as they are sharing the force and only half the force is applied to each spring.

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20
Q

What happens to the extension when the springs are in series?

A

The extension doubles because the same force is being applied to each spring.

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21
Q

What is elasticity?

A

The property of a solid that enables it to regain its original shape after the force is removed

22
Q

What is plasticity?

A

This describes the deformation of a material after the elastic limit is exceeded. The material can longer regain its original shape once it is plastically deformed

23
Q

What is stiffness?

A

This is the measurement of a material’s resistance to changes in size or shape. Also known as the spring constant.

24
Q

What is ductility?

A

The ability for a material to easily stretch without breaking.

25
Q

What is brittleness?

A

It is the ability for a material to snap without stretching or bending when subjected to stress and the elastic limit is exceeded.

26
Q

What happens to the energy that is used to stretch a spring?

A

The energy is stored as elastic potential energy

27
Q

How can you calculate the energy stored in a stretched spring?

A

Energy= (forceextension)/2
or
Energy = (spring constantextension^2)/2

28
Q

What is the equation for stress?

A

stress = force/cross-sectional area

29
Q

What is the equation for strain?

A

strain = extension/original length

30
Q

Why does strain have no unit?

A

It is a ratio

31
Q

What is the Young Modulus?

A

It is a constant value of a material

Measured in Nm^-2(the unit of stress)

32
Q

What is the equation for the Young Modulus?

A

Young Modulus = tensile stress/tensile strain

33
Q

What happens at the yield point on a stress/strain graph?

A

The material stretches without any extra load

The yield point is the stress at which a large amount of plastic deformation takes place with a constant or reduced load

34
Q

What happens at the elastic limit?

A

The material starts to behave plastically

from this point onwards, the material would no longer return to its original shape once the stress is removed.

35
Q

What happens at the limit of proportionality?

A

The material stops obeying Hooke’s law but would still return to its original shape if the stress is removed

36
Q

What happens to brittle items when the stress applied reaches the elastic limit?

A

The material fractures and doesn’t behave plastically

37
Q

Give examples of brittle items

A

Ceramics
glass
Nylon

38
Q

How can you calculate the Young modulus from a stress/strain graph?

A

The constant gradient, where the material obey’s Hooke’s law, is the young modulus of the material

39
Q

Why is the unloading line parallel to the loading line?

A

The stiffness constant,k, is the same

40
Q

Why doesn’t the unloading curve return to the origin?

A

The wire was stretched beyond its elastic limit and deformed plastically
it has been permanently stretched

41
Q

How can you calculate the work done to permanently deform the wire?

A

energy stored + heat lost = total work done

42
Q

What is the ultimate tensile stress?

A

This is the maximum stress that the material can withstand

43
Q

What is the breaking stress?

A

The stress that causes the atoms to completely separate and the material breaks

44
Q

When does elastic deformation happen?

A

Before the elastic limit is reached

45
Q

When does plastic deformation happen?

A

When the elastic limit is exceeded

46
Q

What happens during elastic deformation?

A
  • the atoms of the material are pulled apart when the material is under tension
  • atoms move small distances without changing positions in the material
  • once the load is removed, the atoms return to their original distance apart
47
Q

What happens during plastic deformation?

A
  • some atoms in the material move position relative to one another
  • when the load is removed, the atoms don’t return to their original positions
48
Q

How can you calculate the strain energy?

A

(stress*strain)/2
OR
(force extension/arealength)/2

49
Q

What happens beyond the elastic limit?

A

Some of the energy that caused the plastic deformation cannot be regained and is transformed into thermal energy

50
Q

How can you tell if a material is ductile or not from a stress/strain graph?

A

Ductile materials have yield points and a large extension is produced when a small amount of extra stress is added

51
Q

How can you calculate the work done from stress/strain graphs?

A

The area between the loading and unloading curves is the work done to permanently stretch the material

52
Q

How can the Young’s Modulus of a metal wire be obtained accurately from an experiment?

A

Measurements of the metal wire
-the original length of the wire
-the diameter of the wire
-the extension each time a force is added(increase the force in steps e.g 100g weights intervals
Accuracy of results
-repeat readings
-measure the diameter of the wire in several places and calculate the average
Plot the results on a stress/strain graph
calculate the gradient (the Young’s Modulus)

A level physics (15 decks)

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