Physics Form 4: Chapter 4 - Thermal Equilibrium
When two substances having different temperatures are introduced or kept together, heat
energy flows from a substance at higher temperature to a substance at lower temperature.
Also, heat continues to be transferred till their temperatures are equalized.
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Thermal equilibrium is the situation where there is no net heat flow between the
two bodies at the same temperature.
That is the rate of heat absorption equals to the rate of heat dissipation at the same
temperature.
Two bodies are said to be in thermal equilibrium when:
a) they are at same temperature
b) the net rate of heat flow between them is zero.
Physics Form 4: Chapter 4 - Specific Heat Capacity
Specific Heat Capacity is the amount of energy (in Joules) needed
to increase the temperature of 1 kg of a substance by 1 degree
Celsius
Different material have different specific heat capacity value
High specific heat capacity ===> good insulator of heat
Low specific heat capactiy ===> good conductor of heat
Physics Form 4: Chapter 4 - Latent Heat
Latent heat is the quantity of heat absorbed or released by a substance to change its
physical state without any change in temperature.
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Specific latent heat of fusion is the quantity of heat needed to change 1kg of a
solid to liquid at its melting point without change in temperature.
The temperature does not change even though heat is being absorbed by the solid
particles. This is because the heat absorbed does not increase the kinetic energy of
particles but is used to overcome the force of attraction between the particles.
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Specific latent heat of vaporization is the quantity of heat needed to change 1kg of
a liquid to gas at its boiling point without change in temperature.
The temperature does not change even though heat is being absorbed by the liquid
particles. This is because the heat absorbed does not increase the kinetic energy of
particles but is used to overcome the force of attraction between the particles.
Specific latent heat of vaporization is greater than its specific latent heat of fusion
because:
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More energy is required to break the bonds between liquid molecules in order to
change into gas phase.
Extra energy is required to overcome atmospheric pressure.
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Energy is used to overcome the surface tension of a liquid when its molecules
change into the gas phase.
Physics Form 4: Chapter 4 - Boyle's Law of Gas
Boyle's law states that the pressure of a fixed mass of gas is inversely proportional to
the volume of gas provided the temperature of the gas is constant.
The law was first proposed in 1662 by Robert Boyle
Because pV = constant that means that p1V1 = constant and so does p2V2. We can
therefore write:
where
V1 = equals the original volume,
V2 = equals the new volume,
p1 = the original pressure, and
p2 = the new pressure.
Explanation of Boyle's law by the kinetic theory:
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At constant temperature, the average kinetic
energy of the gas molecules is constant.
When the gas is compressed, the volume is
decreased. Therefore, the number of molecules
per unit volume will increase.
The rate of collision of the gas molecules with the
wall of container will increase.
Thus, the pressure of gas increases.
Physics Form 4: Chapter 4 - Absolute Temperature
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Temperature is a measure of the average kinetic energy of a system particles.
When temperature rises, the average kinetic energy of particles also increases.
Temperature is the degree of hotness, a measure of heat intensity.
Absolute temperature is based on the Kelvin scale. Units on the Kelvin scale are called
Kelvins (K) and no degree symbol is used.
The concept of an absolute zero of temperature evolved in connection with experiments
with gases. When a fixed mass of gas is cooled at a constant pressure (volume), its
volume (pressure) decreases with its temperature. A plot of the experimental values of
volume (pressure) versus temperature can be extrapolated to cross the temperature axis
when the volume (pressure) would be zero. The temperature is the absolute zero of
temperature. It is -273.15 °C, or more approximately -273 °C.
What happens to the matter at absolute zero temperature?
At absolute zero temperature, it's the point at which particles have a minimum energy.
Near absolute zero, the matter stops acting the way it should and starts exhibiting some
strange properties. Some types of matter become superconducting, carrying electric
current with absolutely no resistance, and some of them, like helium, become superfluid
at this temperature, exhibiting absolutely no friction, becoming a Bose-Einstein
Condensate (BEC). This means that a droplet of superfluid helium can rotate inside a
container forever, as if it were in a vacuum.
So far, this temperature has never been achieved, and in theory it could never be achieved.
In 1994, the NIST achieved a record cold temperature of 700 nK (billionths of a kelvin).
In 2003, researchers at MIT eclipsed this with a new record of 450 pK (0.45 nK).
Physics Form 4: Chapter 4 - Charles's Law of Gas
Charles's law states that for a fixed mass of ideal gas, the volume is directly proportional
to its absolute temperature at constant pressure.
Explanation of Charles law by the kinetic theory
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When the temperature of a gas in an enclosed
cylinder is raised, the gas molecules receive heat
energy and their average kinetic energy increases.
This means that molecular velocity will increase
and the frequency of collision between the
molecules and the wall of the cylinder also
increases. Thus, the gas pressure increases.
Increase in pressure will cause the piston to be
pushed up and this indicates that the volume of
the gas has increased.