Notes for Physics EDEXCEL Unit 5 are available for download
The notes contain:
- Solid,liquid and gases.
- Particle model.
Unit 5: Solid, Liquid and gases
Density:
Mass per unit volume.
Given the symbol (rho- ρ) is calculated using:Unit: kg/m3
Practical to calculate the density of a Solid material:
Measure the mass using
suitable equipment (electronic balance)
Measure the volume. Volume of a regularly shaped solid can be measured using ruler. For irregularly shaped objects, immerse the object in water-shown below.
Use the formula and find the
density of a material.
Practical to calculate the density of a Liquid material:
a) Record the mass of an empty 100 ml measuring cylinder using
electronic balance.
b)
Then pour 20 ml of liquid in
the cylinder and record the mass of cylinder with liquid.
c)
Calculate the mass of the
liquid by subtracting empty cylinder value from the 20 ml liquid. (Always
measure from the eye level-shown below in picture).
d) Add 20 ml more to the liquid a repeat the process till 5 pair of
values have been achieved.
e) Then calculate the density and take the average.
Pressure:
Calculated using:
Unit: Pa (pascal) or N/m2
Pressure in liquids:
Important for sea divers, as
when they dive into water, the pressure inside the sea increases by 1 atm for
every 10 m below the surface of water. This changes in pressure causes gases to
diffuse more quickly inside and outside the blood which is harmful for human body,
especially for the ears and lungs.
Increase of pressure with depth:
Diver is affected mainly by
the weight of water above them. When the diver goes deeper the height and
weight increases. So, the pressure on also increases.
Calculated using:
H=height.
Ρ=Density,
kg/m3.
G=gravitational field= 10N/kg
Atmospheric pressure:
Measured using mercury
barometer, how we can measure atmospheric pressure using a mercury. A small
space of vacuum above barometer in order to support the large atmospheric
pressure exerted at 76 cm long mercury. Pressure at X = pressure at Y,
in the diagram.
When large pressure is exerted using a small area the pressure is exerted in the direction of force. Example: hitting nail with hammer, pushing a piston filled with liquid downwards increases the force in the liquid molecules.
Hydraulic machines
Used to transmit pressures
and help in lifting heavier weight using smaller weights.
Manometer
This device helps measure pressure of a gas supply. There are two
points of references (X and Y) which are at the same level pf the liquid which
means that the pressures at X and Y are both same.
As shown in picture:
Pressure X= gas supply
pressure
Pressure Y= atmospheric
pressure + pressure due to 27.2 cm of water. This shows that gas supply
pressure is more than the atmospheric pressure by pressure exerted by 27.2 cm
height of water.
States of matter: Solids, liquids
and gases:
Solid: Atoms are packed regularly
structure and cannot move. They are in fixed shape but they can vibrate. The
atoms are held together by strong forces. Density is the highest compared to
liquid and gases as there is a lot of mass in small volume same as liquid.
Liquid: Atoms are close together and
forces between the molecules keep them closer together. Atoms move from one
place to another. This allows change of shape to fit into the shape of container.
Molecules are closer together which makes it harder to compress. Density is
higher than gases.
Gas: The atoms are far apart and
the forces between them is very small. Atoms are in random constant motion.
Gases can fill any volume and can be compressed easily than solids and liquids.
Density is the lowest compared to solid and liquid. There will be least amount
of mass in the same volume of sample. Density of air is more than that of
hydrogen as air contains atoms of nitrogen and carbon which are more in mass.
Energy:
Internal energy: energy
stored in atoms molecules is known as internal energy. This energy is mainly is
in kinetic form of energy and some amount of potential energy.
Heating:
This changes the energy
stored within a system and increases the temperature. When a gas is heated, the
atoms move faster and kinetic energy of atoms increases.
This heating change also
causes a change of state.
Solid on heating turns to liquid. (There is a slight increase in volume as atoms move away from each other, which increase the potential energy, so the internal energy also increases
Changes of state is described
using the words below:
Melting: Solid turns
to liquid, The internal energy increases.
Freezing: Liquid turns
to a solid, internal energy of system decreases.
Boiling/evaporation: Liquid
turns to gas, internal energy increases.
Condensation: gas turns to
liquid, Internal energy decreases.
Sublimation: Solid turns
to directly to gas, internal energy increases. Solid CO2 (dry ice) turns
directly to gas.
Deposition: reverse
process of sublimation, gas to solid internal energy decreases. These changes
of state are a physical change and are reversible, as the mass does not change
in a reaction but internal energy changes.
Investigation:
Cooling curve, temperature against time:
Initially, temperature drop
is quick and then the decrease in temperature slows down. Example: Icing of a liquid.
Method:
a) A tripod stand with gauze is set-up. A beaker filled with 150 ml
of water is kept.
b) Test-tube is put into stearic acid into clamp supported by a
retort stand. A cotton wool or mineral fibre plug is kept at the tube neck to
reduce fumes.
c)
Table is made to record the
pair of recordings of temperature and time (in mins).
d) Bunsen burner is lit a water is boiled. Stearic acid is placed
into water. Avoid heating the tube directly in Bunsen flame.
e) Using the thermometer measure the temperature till it reaches 100°C.
f)
Start the stopwatch and move
the stearic acid quickly back to retort stand.
g) Record the temperature/ min till it reaches 50°C.
h) Plot a graph of temperature against time.
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