Download Section 3. Matter Course Notes

A-Level Course Notes: PHYSICS
SECTION III: Matter
SECTION III
Matter
CIE A-Level [AS and A2]
________________________
Course Notes
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A-Level Course Notes: PHYSICS
SECTION III: Matter
Syllabus Details______________________
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A-Level Course Notes: PHYSICS
SECTION III: Matter
9. Phases of Matter [AS]______________________
Content
9.1 Density
9.2 Solids, liquids, gases
9.3 Pressure in fluids
9.4 Change of phase
Learning outcomes_____________________________________
Candidates should be able to:
(a) define the term density
Density (kgm-3) = mass (kg) / volume (m3)
(b) relate the difference in the structures and densities of solids, liquids and gases to
simple ideas of the spacing, ordering and motion of molecules
(c) describe a simple kinetic model for solids, liquids and gases
Liquid
Solid
Gas
Increasing Kinetic Energy
• Fixed volume
• Fixed shape
• Molecules held in position
by strong bonds
• Molecules vibrate about
fixed position
• Higher temp = higher
vibrations
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• Fixed volume
• Shape of container
• Molecules can vibrate and
move but are held close
together by strong bonds
• Expands to fill container
• Molecules can vibrate and
move around freely
• Only very weak bonds exist
between molecule
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A-Level Course Notes: PHYSICS
SECTION III: Matter
(d) describe an experiment that demonstrates Brownian motion and appreciate the
evidence for the movement of molecules provided by such an experiment
Smoke (oil droplets)
Brownian Motion
Path of one droplet



Smoke (oil droplets) are seen to move randomly
This motion is evidence that the air particles are also moving randomly and
colliding with the smoke droplets
The air particles cannot be seen but their motion can be understood by the smoke
droplets which can be seen
(e) distinguish between the structure of crystalline and non-crystalline solids with
particular reference to metals, polymers and amorphous materials
Crystalline
Non - crystalline
• regular repeating pattern
• no regular repeating pattern
Polymers
Metals
• Amorphous
Amorphous Materials
• no regular repeating pattern
(eg glass)
• poly-crystalline
• Semi-crystalline
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A-Level Course Notes: PHYSICS
SECTION III: Matter
(f) define the term pressure and use the kinetic model to explain the pressure
exerted by gases
Pressure (Pa) = Force (N) / Area (m2)
Pa = Nm-2
Kinetic model
• Molecule collides with wall
• Momentum changes
• Force on molecule from wall
• Equal and opposite force on wall from
molecule
• This averages over time to a constant
force on the wall
• The force per unit area of the wall is the
pressure
Force on
molecule
Force on wall
(g) derive, from the definitions of pressure and density, the equation p = ρgh
(h) use the equation p = ρgh
Liquid column
Area = A
Density = r
Height = h
Weight =F
Hydrostatic Pressure
Density:
r=m/V
Pressure:
p = F/A
Volume of column:
V = Ah
Weight of column:
F = mg
F = rghA
h
Hydrostatic pressure p = rgh
A
F
This formula is given at the start of the test paper
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A-Level Course Notes: PHYSICS
SECTION III: Matter
PHASE CHANGE
Temperature
(i) distinguish between the processes of melting, boiling and evaporation.
B oiling
PHASE CHANGE
Condensing
Melting
Freezing
SOLID
LIQUID
GAS
Time
Number
At the phase changes the random kinetic energy of the molecules does not change,
but the potential energy does. Intermolecular bonds are being broken which
requires energy.
Enough energy
to Evaporate
Energy
A. At all temperatures there will be a distribution of kinetic
energy within the liquid.
B. Molecules with high kinetic energy can ‘escape’ the
liquid and become a gas: Evaporation.
C. The average speed of the molecules in the liquid will
decrease: Therefore, the temperature of the liquid will
decrease.
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A-Level Course Notes: PHYSICS
SECTION III: Matter
10. Deformation of Solids [AS]_________________
Content
10.1 Stress, strain
10.2 Elastic and plastic behaviour
Learning outcomes_____________________________________
Candidates should be able to:
a) appreciate that deformation is caused by a force and that, in one dimension, the
deformation can be tensile or compressive
Deformations caused by forces
F
F
Tensile Deformation
F
Compressive
Deformation
F
(b) describe the behaviour of springs in terms of load, extension, elastic limit,
Hooke’s law and the spring constant (i.e. force per unit extension)
No
Force
10N
Force
20N
Force
String
F= k x
Hooke’s Law: Up to the elastic limit the extension
of a spring is proportional to the tension force. The
constant of proportionality is called the spring
constant (k)
Extension / m
Elastic Limit
force / N
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A-Level Course Notes: PHYSICS
SECTION III: Matter
SEE PHET SIM
(c) define and use the terms stress, strain and the Young modulus
Area = A
F
F
Length = l0
Dl
F
F
Tensile stress = force / area
 = F/A
Tensile strain = extension / original length
 = Dl / l0
Young’s modulus = Tensile stress / Tensile strain
E=
[Nm-2]
[Nm-2]
(d) describe an experiment to determine the Young modulus of a metal in the form
of a wire
wire
pulley
0
10
20
30
40
masses

Using the apparatus above measure the extension of the wire with added
masses
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A-Level Course Notes: PHYSICS
SECTION III: Matter
(e) distinguish between elastic and plastic deformation of a material
Elastic deformation: Material returns to its original shape when forces are
removed
Plastic deformation: Material does NOT return to its original shape when forces
are removed
(f) deduce the strain energy in a deformed material from the area under the forceextension graph
Force / N
Area under graph = Strain Energy
Extension / m
(g) demonstrate knowledge of the force-extension graphs for typical ductile, brittle
and polymeric materials, including an understanding of ultimate tensile stress.
Ductile Material
Force
Force
Fracture
Fracture
Extension
Extension
Force
Brittle Material
Ultimate Tensile Stress
Polymer Material
Extension
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A-Level Course Notes: PHYSICS
SECTION III: Matter
11. Ideal Gases [A2]__________________________
Content
11.1 Equation of state
11.2 Kinetic theory of gases
11.3 Pressure of a gas
11.4 Kinetic energy of a molecule
Learning outcomes_____________________________________
Candidates should be able to:
(a) recall and solve problems using the equation of state for an ideal gas expressed
as pV = nRT (n = number of moles)
The equation of state for an ideal gas is
PV = nRT
P = Pressure
V = Volume
T = Temperature
R = universal gas constant
n= number of moles
(b) infer from a Brownian motion experiment the evidence for the movement of
molecules
Smoke (oil droplets)
Brownian Motion
Path of one droplet



Smoke (oil droplets) are seen to move randomly
This motion is evidence that the air particles are also moving randomly and
colliding with the smoke droplets
The air particles cannot be seen but their motion can be understood by the smoke
droplets which can be seen
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A-Level Course Notes: PHYSICS
SECTION III: Matter
(c) state the basic assumptions of the kinetic theory of gases
Kinetic model of ideal gas
• Molecule collides with wall
• Mo mentum changes
• Force on molecule fro m wall
• Equal and opposite force on wall fro m
molecule
• This averages over time to a constant
force on the wall
• The force per unit area of the wall is the
pressure
Assumptions:
• Newton’s law apply to molecules
• No intermolecular forces
• The molecules are perfect spheres
(treated as points)
• The molecules are in random motion
• The collisions between the molecules
are elastic (no energy lost)
• There is no time spent in these
collisions
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Force on
mo lecule
Force on wall
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A-Level Course Notes: PHYSICS
SECTION III: Matter
(d) explain how molecular movement causes the pressure exerted by a gas and hence
deduce the relationship p = 1/3Nm/V < c 2 >
(N = number of molecules) [a rigorous derivation is not required]
L
Cx



Consider a cube of space with length L
Consider a particle moving in one dimension x with velocity cx
When the particle collides with the wall its velocity is reversed so its
change in momentum is equal to...
o Dpx = 2mcx

The time between collisions with each wall of the cube is equal to...
o Time between collisions = 2L / cx

The rate at which momentum is transferred to the wall is...
o Rate of change of momentum = 2mcx / (2L/cx) = mcx 2 / L

If there are N particles in the cube the total force is...
o Total force = Nmcx 2 / L

Pressure is force over area so pressure is...
o Pressure on one wall is Nmcx 2 / L3

L3 is the volume so...
o Pressure = Nmcx 2 / V


The average of cx 2 can be written as < cx 2>
As all directions, x, y and z can be considered equal
o < cx 2> = 1/3< c 2>

Hence
o P = 1/3Nm<c 2> / V
This formula is given at the start of the test paper
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A-Level Course Notes: PHYSICS
SECTION III: Matter
(e) compare pV = 1/ 3 Nm < c 2 > with pV = NkT and hence deduce that the average
translational kinetic energy of a molecule is proportional to T.

The average translational Ek of the particles can be expressed as ...
o <Ek> = 1/2m< c2>

Combining with P = 1/3Nm<c 2> / V we get....
o pV = 2/3N(1/2m< c2>) = 2/3N<Ek>

Combining this with pV = NkT we get...
o pV = 2/3N<Ek> = NkT
o <Ek> =3/2kT

Therefore, Temperature is proportional to Average translational kinetic
energy
12. Temperature [A2]________________________
Content
12.1 Thermal equilibrium
12.2 Temperature scales
12.3 Practical thermometers
Learning outcomes_____________________________________
Candidates should be able to:
(a) show an appreciation that thermal energy is transferred from a region of higher
temperature to a region of lower temperature
(b) show an understanding that regions of equal temperature are in thermal
equilibrium
Temperature is a property that determines the direction of thermal energy transfer
between two bodies in thermal contact.
Thermal energy is transferred from ‘hot’ object to ‘cold’ object until they have
reached the same temperature, this is thermal equilibrium.
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A-Level Course Notes: PHYSICS
SECTION III: Matter
Property X
(c) show an understanding that a physical property that varies with temperature
may be used for the measurement of temperature and state examples of such
properties
t? =
(Xt – XL)
N + tL
(XH – XL)
N = Number of divisions between XH and XL
XH = value of property at higher fixed point
XL = value of property at lower fixed point
tL
tH
XH
Xt
XL
t?
Temperature
Example properties...


Expansion of a liquid (mercury)
Electrical resistance
(d) compare the relative advantages and disadvantages of resistance and
thermocouple thermometers as previously calibrated instruments
Thermometer
Resistance
Thermocouple
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Advantage
Wide range
Over short ranges variation
is linear
Very sensitive
Large sensitivity range
Small device so rapid
response
Disadvantage
Variation is not linear over
long ranges, so needs
calibration at a number of
temps.
Variation not linear
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A-Level Course Notes: PHYSICS
SECTION III: Matter
(e) show an understanding that there is an absolute scale of temperature that does
not depend on the property of any particular substance (i.e. the thermodynamic
scale and the concept of absolute zero)
Volume / m3
Constant pressure
-273oC
Temperature / oC
Volume / m3
Absolute Zero
0K



Temperature / K
All gases have variations of volume with temperature that extrapolate back
to –273oC at zero volume.
This can be described as absolute zero as we can not imagine a –ve
volume.
This absolute zero forms the basis of the Kelvin scale where absolute zero
is defined as 0 Kelvin (0K).
(f) convert temperatures measured in kelvin to degrees Celsius and recall that T / K
= T / °C + 273.15
T/K = t/oC + 273
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A-Level Course Notes: PHYSICS
SECTION III: Matter
13. Thermal Properties of Materials [A2]________
Content
13.1 Specific heat capacity
13.2 Specific latent heat
13.3 Internal energy
13.4 First law of thermodynamics
Learning outcomes_____________________________________
Candidates should be able to:
(a) explain using a simple kinetic model for matter why
• melting and boiling take place without a change in temperature



Temperature is a measure of the average random EE of the particles
At a phase transition supplied energy is used to break bonds
No change in KE occurs so temperature does NOT change
• the specific latent heat of vaporisation is higher than specific latent heat of
fusion for the same substance


Fusion is from a solid to a liquid and vaporisation from a liquid to a gas
More bonds are broken in vaporisation so the specific latent heat is higher
• a cooling effect accompanies evaporation


As the particles which evaporate are those with a higher velocity and so
KE the average KE of the substance decreases
As temperature is a measure of average KE the temperature decreases
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A-Level Course Notes: PHYSICS
SECTION III: Matter
(b) define and use the concept of specific heat capacity, and identify the main
principles of its determination by electrical methods
Thermal Capacity
The energy required to raise the temperature of an object by 1K
C=
DQ
DT
DQ = change in energy
DT = change in temperature
(J K -1 )
Specific Heat Capacity
The energy required to raise a unit mass of a substance 1K
c=
DQ
m DT
(J kg-1 K-1 )
Electrical Method
Heater
Object
V
A
c=
ItV
Variable power supply
m(T2-T1)
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A-Level Course Notes: PHYSICS
SECTION III: Matter
(c) define and use the concept of specific latent heat, and identify the main principles
of its determination by electrical methods
Specific Latent Heat
The amount of energy per unit mass absorbed or released
during a change of phase
l=
DQ
m
(J kg-1)
Vaporization
A
V
l=
ItV
m1 – m2
Heater
00250.0g
(d) relate a rise in temperature of a body to an increase in its internal energy
(e) show an understanding that internal energy is determined by the state of the
system and that it can be expressed as the sum of a random distribution of kinetic
and potential energies associated with the molecules of a system
Internal Energy = Total Potential Energy + Total Kinetic Energy
Random Kinetic Energy = Translational Kinetic Energy + Rotational Kinetic
Energy
Translational energy is the energy associated with the whole molecule moving
in a certain direction.
Rotational energy is the energy associated with the molecule rotation around a
certain point.
Potential energy is the energy associated with intermolecular forces.
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A-Level Course Notes: PHYSICS
SECTION III: Matter
(f) recall and use the first law of thermodynamics expressed in terms of the increase
in internal energy, the heating of the system and the work done on the system.
THERMODYNAMIC SYSTEM: For the study of ideal gases, the gas being
considered is the system.
THE SURROUNDINGS: Everything other than the gas is the surroundings.
DQ = DU + D W
DQ = Thermal energy given to system
DU = Internal energy
DW = Work done
DQ
DU
DW
+ve
Thermal energy going into system
-ve
Thermal energy going out of system
+ve
Internal energy of system is increasing
-ve
Internal energy of system is decreasing
+ve
System is doing work
-ve
Surroundings doing work
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A-Level Course Notes: PHYSICS
SECTION III: Matter
Background Reading_________________
PHYSICS, Giancoli 6th edition, Chapter 11 and 24
Useful Websites______________________
http://phet.colorado.edu/en/simulations/category/new
http://www.s-cool.co.uk/alevel/physics.html
http://www.physicsclassroom.com/mmedia/index.cfm
http://www.phys.hawaii.edu/~teb/java/ntnujava/index.html
http://www.colorado.edu/physics/2000/index.pl
Constants___________________________
[These are given on each test paper]
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