4. Brownian Motion:
the erratic random movement of microscopic
particles in a fluid, as a result of continuous
bombardment from molecules of the surrounding
medium.
Robert Brown (1773 - 1858)
(born Montrose, Scotland 21 December 1773 -
died at Soho Square, London, 10 June 1858)
5. Energy of particles
• Most of us use the word ‘heat’ to mean something
that feels warm, but science defines heat as the
flow of energy from a warm object to a cooler
object.
• Actually, heat energy is all around us – in
volcanoes, in icebergs and in your body. All
matter contains heat energy.
• Heat energy is the result of the movement of tiny
particles called atoms, molecules or ions in
solids, liquids and gases. Heat energy can be
transferred from one object to another, and the
transfer or flow due to the difference in
temperature between the two objects is called
heat.
• For example, an ice cube has heat energy and so
does a glass of lemonade. If you put the ice in the
lemonade, the lemonade (which is warmer) will
transfer some of its heat energy to the ice. In
other words, it will heat up the ice. Eventually, the
ice will melt and the lemonade and water from the
ice will be the same temperature. This is known
as reaching a state of thermal equilibrium.
• The internal energy of a system is the sum of
all kinetic and potential energy in a system.
6. Temperature
• Class activity: page 103, question 1 and 4.
• What is temperature?
• Temperature (symbolized T ) is an expression of
heat energy. Temperature can mean different
things in different situations.
• Thermodynamic temperature is a measure of the
kinetic energy in molecules or atom s of a
substance. The greater this energy, the faster the
particles are moving, and the higher the reading
an instrument will render. This is the method lay
people most often use.
• Absolute zero and the kelvin scale:
• Absolute zero is the lowest possible temperature
where nothing could be colder and no heat
energy remains in a substance. By international
agreement, absolute zero is defined as precisely;
0 K on the Kelvin scale, which is a
thermodynamic (absolute) temperature scale; and
–273.15 degrees Celsius on the Celsius scale.
• The Celsius scale:
• The freezing point is taken as 0 degrees Celsius
and the boiling point as 100 degrees Celsius. The
Celsius scale is widely known as the centigrade
scale because it is divided into 100 degrees. It is
named for the Swedish astronomer Anders
Celsius, who established the scale in 1742.
7. thermometers
Definition of thermometer. : an instrument for
determining temperature; especially : one consisting of
a glass bulb attached to a fine tube of glass with a
numbered scale and containing a liquid (as mercury or
colored alcohol) that is sealed in and rises and falls with
changes of temperature.
Types of thermometer:
1. Clinical [liquid-in-glass] thermometer
2. Electrical thermometer
a. Resistance thermometer
i. Platinum resistance
ii. Thermistors
b. Thermocouple
3. Non-contact infrared radiation thermometers
4. Non-contact thermal imaging and thermography
Thermal imaging is now widely used in:
a. surveillance
b. night vision
c. search and rescue
d. building and land surveying
e. aircraft and missile tracking
f. detecting hot spots due to failure in electrical
equipment and electronic circuits
g. medical thermography
Platinum Resistance
Thermistors for
use in current
limiting circuits
8. Type Measured Property Temperature Range Features
Liquid-in-glass thermometer Thermal expansion of the liquid -100 ºC to 300 ºC Can break!
Electrical resistance thermometer
Platinum resistance
Standard Platinum Resistance
(SPRT)
Industrial platinum resistance
(IPRT, PT100s, RTD (resistance
temperature detector)
Thermistor
Electrical resistance -250 ºC to 600 ºC Very accurate
Laboratory use
Industrial use
Small probes, fast response, but
limited temperature changes.
Thermocouple thermometer
Voltage generated by 2 wires made
out of different metals
-200 °C to 2000 °C
Cheapest and most common
Radiation thermometers
Intensity of infrared (heat) radiation
given out by an object
-400 °C to 3000 °C No need to contact the object to
measure its temperature
Choosing a thermometer
Different types of thermometers are used in a wide range of applications and situations. Factors to be considered include size, accessibility
and required temperature ranges.
9. Assignment:
1. in a tabular form. Compare the liquid-in-glass thermometer with regards to;
sensitivity, range, responsiveness and linearity.
2. which liquid is most effective to be used?
EXPANDING SOLIDS, LIQUIDS AND GASES:
All three states of matter (solid, liquid and gas)
expand when heated. The atoms themselves do not
expand, but the volume they take up does.
When a solid is heated, its atoms vibrate faster
about their fixed points. The relative increase in the
size of solids when heated is therefore small. Metal
railway tracks have small gaps so that when the sun
heats them, the tracks expand into these gaps and
don’t buckle.
Liquids expand for the same reason, but because
the bonds between separate molecules are usually
less tight they expand more than solids. This is the
principle behind liquid-in-glass thermometers. An
increase in temperature results in the expansion of the
liquid which means it rises up the glass.
Molecules within gases are further apart and weakly
attracted to each other. Heat causes the molecules to
move faster, (heat energy is converted to kinetic
energy) which means that the volume of a gas
increases more than the volume of a solid or liquid.
However, gases that are contained in a fixed volume
cannot expand - and so increases in temperature
result in increases in pressure.
10. Examples of devices that operates on expansion:
1. A bimetallic strip is used to convert a
temperature change into mechanical
displacement. The strip consists of two strips of
different metals which expand at different rates as
they are heated, usually steel and copper, or in
some cases steel and brass.
Bimetallic strip is used in various devices such as:
• Thermostats: in the thermostats one end of the
bimetal strip is mechanically fixed and attached to
a power source while the other moving end
carries an electrical contact. In adjustable
thermostats another contact is positioned with a
regular lever. The position so set controls the
regulated temperature
• Clocks: bimetallic construction is used for the
circular rim of the balance wheel of a clock or
watch.
• Thermometer: bimetallic is wrapped into coil,
one end of the coil is fixed to the housing of the
device and the other drives an indicating needle
• Fire alarm: in the fire alarm, the bimetallic strip is
placed as a switch. When the temperature in the
room increases due to fire, the bimetallic strip
bends and the circuit is complete and the alarm is
triggered off for people to know there is fire.
• Electrical devices: in miniature circuit breakers,
bimetallic strips are used to protect circuits from
excess current. The bimetallic strip is widely
used in many electrical circuits to serve as a
thermostat switch. It controls the temperature in
the device by turning on or off
2. Water and ice:
• When liquid water is cooled, it contracts like one
would expect until a temperature of approximately
4 degrees Celsius is reached. After that, it
expands slightly until it reaches the freezing point,
and then when it freezes it expands by
approximately 9%.
11. • State changes
• Changes of state are:
solids melting into liquids
• liquids boiling into gases
• gases condensing into liquids
• liquids freezing or solidifying into solids
Evaporation is sometimes confused with boiling.
They both involve liquids turning to gases, but
evaporation is different because:
• it occurs at any temperature - not just the boiling
point
• it only happens at the surface of the liquid - not
throughout like boiling
• boiling requires an energy input - whereas
evaporation is the release of the molecules with
the highest energy
• Evaporation cools liquids as a result of this
energy loss. Evaporation is increased by higher
temperatures, a greater surface area or a draft
over this surface area.
• A substance must absorb heat energy so that it
can melt or boil. The temperature of the
substance does not change during melting,
boiling or freezing - even though energy is still
being transferred.
• Heating curves and cooling curves
A heating curve is a graph showing the temperature of
a substance plotted against the amount of energy it
has absorbed. You may also see a cooling curve,
which is obtained when a substance cools down and
changes state.
A heating curve for ice
• The temperature stays the same when a solid is
melting or a liquid is boiling (changing state)
during a change of state, even though heat
energy is being absorbed.
• The temperature also stays the same while a
liquid freezes, even though heat energy is still
being released to the surroundings.
12. Thermal conduction: activity-page 113 Q1,2 and 5.
Thermal conduction is the transfer of heat (internal
energy) by microscopic collisions of particles and
movement of electrons within a body.
Heat conduction, also known as thermal conduction,
is the process where heat is transferred within a body
due to the collision of neighbouring particles
To increase the thermal conduction;
• Increase the temperature difference between the
ends of the bar
• Increase the cross-sectional area of the bar
• Reduce the length of the bar.
Thermal conductors and insulators:
• Metal is a good thermal conductor, while plastic is
a poor thermal conductor. An insulator is a
material that does not allow a transfer of
electricity or energy. Materials that are poor
thermal conductors can also be described as
being good thermal insulators.
Using insulating materials:
• In building construction
• In house-hold utensils
• In animals
How metals conduct:
• metals generally conduct heat better than other
solids do. In metals, some of the electrons (often
one per atom) are not stuck to individual atoms
but flow freely among the atoms. that's why
metals are such good conductors of electricity.
Now if one end of a bar is hot, and the other is
cold, the electrons on the hot end have a little
more thermal energy than the ones on the cold
end. So as the electrons wander around, they
carry energy from the hot end to the cold end,
which is another way of saying they conduct heat.
• how fast they conduct heat depends a lot on
things like how many free electrons are around,
how fast they move, and especially how far they
usually go before they bump into something and
change direction. Those are the same factors that
determine how well the metal conducts electricity.
13. convection
Convection in liquid:
• Liquids and gases are fluids. The particles in these fluids
can move from place to place. Convection occurs when
particles with a lot of heat energy in a liquid or gas move
and take the place of particles with less heat energy. Heat
energy is transferred from hot places to cooler places by
convection.
Convection in air:
Using convection at home:
• Freezer is the source for the refrigerator's coldness. When
the freezer is placed on top, the cold air produced from it
is denser than the warmer air in the bottom. So cold air
being dense sinks down and the warm air is forced to rise
up so when the warm air rises up it and gets cold in the
freezer.
• Activity:
• Explain how the room gets warm with the use of either an
electric heater or charcoal fire
• Explain how the air-conditioner keeps the room cold.
14. Thermal radiation
colour finish ability to emit
thermal radiation
ability to absorb
thermal radiation
dark dull or matt good good
light shiny poor poor
All objects give out and take in thermal
radiation, which is also called infrared
radiation. The hotter an object is, the
more infrared radiation it emits.
Light from the sun reaching earth
Infrared radiation is a type of
electromagnetic radiation that involves
waves. No particles are involved, unlike in
the processes of conduction and
convection, so radiation can even work
through the vacuum of space. This is why
we can still feel the heat of the Sun,
although it is 150 million km away from
the Earth.
Some surfaces are better than others at
reflecting and absorbing infrared
radiation.
Comparison of surfaces abilities to reflect and
absorb radiation
15. • Greenhouse effect
• The greenhouse effect is a natural process that
warms the Earth’s surface. When the Sun’s
energy reaches the Earth’s atmosphere, some of
it is reflected back to space and the rest is
absorbed and re-radiated by greenhouse gases.
• Greenhouse gases include water vapour, carbon
dioxide, methane, nitrous oxide, ozone and some
artificial chemicals such as chlorofluorocarbons
(CFCs).
• The absorbed energy warms the atmosphere and
the surface of the Earth. This process maintains
the Earth’s temperature at around 33 degrees
Celsius warmer than it would otherwise be,
allowing life on Earth to exist.
• Enhanced greenhouse effect
• The problem we now face is that human activities
– particularly burning fossil fuels (coal, oil and
natural gas), agriculture and land clearing – are
increasing the concentrations of greenhouse
gases. This is the enhanced greenhouse effect,
which is contributing to warming of the Earth.
• Greenhouse effect
• Step 1: Solar radiation reaches the Earth's
atmosphere - some of this is reflected back into
space.
• Step 2: The rest of the sun's energy is absorbed
by the land and the oceans, heating the Earth.
• Step 3: Heat radiates from Earth towards space.
• Step 4: Some of this heat is trapped by
greenhouse gases in the atmosphere, keeping
the Earth warm enough to sustain life.
• Step 5: Human activities such as burning fossil
fuels, agriculture and land clearing are increasing
the amount of greenhouse gases released into
the atmosphere.
• Step 6: This is trapping extra heat, and causing
the Earth's temperature to rise.
• What is a greenhouse and what does it do?
• People grow tomatoes and flowers and other
plants in them. A greenhouse stays warm inside,
even during winter. Sunlight shines in and warms
the plants and air inside. But the heat is trapped
by the glass and can't escape.
16. How does climate change affect the greenhouse
effect?
• Because there are more and more greenhouse
gases in the atmosphere, more heat is trapped
which makes the Earth warmer. This is known as
GLOBAL WARMING. A lot of scientists agree that
man's activities are making the natural
greenhouse effect stronger.
• The greenhouse effect is a warming of Earth's
surface and the air above it. It is caused by
gases in the air that trap energy from the sun.
These heat-trapping gases are called greenhouse
gases. The most common greenhouse gases are
water vapor, carbon dioxide, and methane.
Without the greenhouse effect, Earth would be
too cold for life to exist.
• Land, oceans, and plants absorb, or soak up,
energy from sunlight. They release some of this
energy as heat. Greenhouse gases absorb the
heat and then send it back toward Earth.
Without greenhouse gases, this heat would
escape back into space.
• Scientists believe that human activities are
increasing the greenhouse effect. When people
drive a car or operate a factory they burn coal,
oil, and other fossil fuels. This adds extra
greenhouse gases to the air, and the extra gases
trap more heat. Many scientists think that this
has led to global warming, or a steady rise in
the average temperature of Earth's surface.
• Solar panel refers to a panel designed to absorb
the sun's rays as a source of energy for
generating electricity or heating.
• Solar water heating systems use solar panels,
called collectors, fitted to your roof. These collect
heat from the sun and use it to heat up water
which is stored in a hot water cylinder. A boiler or
immersion heater can be used as a back-up to
heat the water further to reach the temperature
you want.
17. A vacuum flask is an insulating storage vessel that
greatly lengthens the time over which its contents
remain hotter or cooler than the flask's surroundings.
• A vacuum flask, or thermos, does not allow heat
transfer by any of the three ways that heat can
travel.
• The insulated stopper reduces conduction and
convection
• The silver coating on the inner bottle prevents
heat transfer by radiation,
• The vacuum between its double wall prevents
heat moving by conduction and convection.
Unit 5.09: liquids and vapour class activity:
• What is the relationship between evaporation,
boiling and condensation?
• Explain the process of cloud formation.
18. Specific heat capacity
Temperature and heat are not the same thing:
• temperature is a measure of how hot something
is
• heat is a measure of the thermal energy
contained in an object.
• Temperature is measured in °C, and heat is
measured in J.
When heat energy is transferred to an object, its
temperature increase depends upon the:
• the mass of the object
• the substance the object is made from
• the amount energy transferred to the object.
For a particular object, the more heat energy
transferred to it, the greater its temperature increase.
Specific heat capacity:
• The specific heat capacity of a substance is the
amount of energy needed to change the
temperature of 1 kg of the substance by 1°C.
• Different substances have different specific heat
capacities.
• Notice that water has a particularly high
specific heat capacity. This makes water
useful for storing heat energy, and for
transporting it around the home using central
heating pipes.
Calculating specific heat capacity:
• Here is the equation relating energy to specific
heat capacity:
• E = m × c × θ
• E is the energy transferred in joules, J
• m is the mass of the substances in kg
• c is the specific heat capacity in J / kg °C
• θ (‘theta’) is the temperature change in degrees
Celsius, °C
Thermal/heat capacity:
Heat capacity (C) is the amount of energy needed to
raise the temperature of a specific substance by 1
degree Celsius. Heat capacity can also be viewed as
the ratio of the amount of energy transferred to an
object and the resultant temperature rise (deltaT).
C = Q / deltaT
19. Latent heat
• Latent heat of a substance is the amount of
energy absorbed or released by the substance
during a change in its physical state that occurs
without changing its temperature.
• SI unit of latent heat is the joule (J).
• The latent heat associated with melting a solid or
freezing a liquid is called the latent heat of fusion
(Lf);
• that associated with vaporizing a liquid or a solid
or condensing a vapour is called the latent heat of
vaporization (Lv).
• Specific latent heat of fusion
• Specific latent heat of fusion, lf, of a substance is
defined as the amount of heat required to change
a unit mass of the substance from solid to liquid
state, without any change in the temperature.
• SI unit of specific latent heat of fusion, lf, is joule
per kilogram (Jkg-1)
• Q=mlfQ=mlf, where
Q = amount of thermal energy absorbed or
released
m = mass of substace
lf = specific latent heat of fusion.
•
Specific latent heat of vapourization
• Specific latent heat of vapourization, lv, of a
substance is defined as the amount of heat
required to change unit mass of the substance
from liquid state to gas state without a
temperature change.
• SI unit of specific latent heat of vapourization, lv,
of a substance is joule per kilogram (Jkg-1)
• Q=mlvQ=mlv , where
Q = amount of thermal energy absorbed or
released
m = mass of substace
lf = specific latent heat of vapourization.
•
• Assignment: page 124 questions 5 and 6.
