This document discusses heat transfer and the three main methods: conduction, convection, and radiation. Conduction involves the direct contact transfer of heat between objects. Convection involves the transfer of heat by the movement of molecules within a substance from warmer to cooler areas. Radiation involves the transfer of heat through space, such as the sun's rays causing sunburn.
Transmission of heat. Conduction, Convection, Radiation, Applications, Workin...Aq Sa
Heat is the thermal energy that flows from an object at higher temperature to an object at lower temperature.
The transfer of heat energy from one object to the other is called transmission of heat. Heat energy transfers in three ways,
1. Conduction
2. Convection
3. Radiation
Conduction
If one end of a metal rod is heated with a flame,
the other end will also get heated up after a while. The heat energy is transferred from one end of the rod to the other without the actual movement of particles (atoms or molecules) of the rod. Such a mode of transmission of heat is called conduction.
The transfer of heat through matter without the actual movement of particles from their position is called conduction.
Conduction occurs in solids, liquids and gases, but solids usually conduct heat better than liquids or gases.
In solids, the particles are held very close to each other. They vibrate constantly. When we heat one part of a solid, the particles gain heat energy and start vibrating faster. During their vibration they collide nearby particles and also cause them to vibrate fast. In this way, the particles of hot part of a solid transfer heat to those in the colder parts.
Good and Bad Conductors
Different materials conduct heat at different rates. Materials which allow heat to flow through them easily are called good conductors of heat. Solids such as metals are good conductors of heat.
Materials which do not allow heat to flow through them easily are called bad conductors of heat or heat insulators. Solids such as wood, glass, plastic, styrofoam, etc. are bad conductors of heat. All liquids (except mercury which is a liquid metal) and gases are also bad conductors of heat.
Why metals are better conductors than non-metals?
All solids (metals and non-metals) are made of tiny particles called molecules. But, some solids conduct heat better than others. Put a metal and a plastic spoon in hot water. Which one is a good conductor of heat, metal or plastic? When both spoons receive heat energy, the particles (atoms or molecules) at the hot end of each spoon vibrate fast and collide into neighbouring particles. These particles transfer heat energy to next neighboring particles.
Particles in metals are packed more closely together than non-metals. Metals can transmit heat energy more readily than non-metals (wood, plastic, etc.). The presence of free electrons also speeds up the transfer of heat in metals. When the metal spoon gets heated, the free electrons gain kinetic energy and move farther towards the colder parts of the metal spoon. They collide the atoms in the colder parts and transfer heat energy to them. In metals, heat energy is transferred from one place to another both by the vibrations of particles as well as by the movement of free electrons. That is why metals are good conductors of heat than non-metals(insulators).
Conduction in Liquids and Gases
The process of conduction in liquids and gases is very slow as compared to solids.
where heat is transfer high in conduction or convection where heat i.docxjbarbara1
where heat is transfer high in conduction or convection
where heat is transfer high in conduction or convection
Solution
CONDUCTION--
Conduction is the transfer of heat between substances that are in direct contact with each other. The better the conductor, the more rapidly heat will be transferred. Metal is a good conduction of heat. Conduction occurs when a substance is heated, particles will gain more energy, and vibrate more. These molecules then bump into nearby particles and transfer some of their energy to them. This then continues and passes the energy from the hot end down to the colder end of the substance.
CONVECTION--
Thermal energy is transferred from hot places to cold places by convection. Convection occurs when warmer areas of a liquid or gas rise to cooler areas in the liquid or gas. Cooler liquid or gas then takes the place of the warmer areas which have risen higher. This results in a continous circulation pattern. Water boiling in a pan is a good example of these convection currents. Another good example of convection is in the atmosphere. The earth\'s surface is warmed by the sun, the warm air rises and cool air moves in.
Hence more heat is transferred by CONDUCTION because of the direct contact.
.
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1. A Form of energy that is related to the K.E.
of molecules. The motion of molecules
produces heat. The more motion, the more
heat is generated.
2. Heat Transfer
The movement of heat (thermal
energy) from a warmer object to a
colder one.
Heat is a moving energy.
There are three forms
of heat transfer:
Conduction
Convection
Radiation
3. The transfer of
heat by direct
contact
between objects
or particles.
5. Heat transferred by
the movement of
molecules within a
substance.
Movement occurs
from warmer areas to
cooler areas.
6. The movement of a substance that is
caused by differences in temperature and
density.
Examples: wind
boiling water
Nature wants everything
to be balanced !!!
7. Conductors are materials that
transfer heat easily.
Examples:
metals like copper
and gold.
8. A pot is a conductor.
The molecules in a
conductor are
close together.
This allows the
heat to move to all
parts of the pot and
the stew in the pot.
9. An insulator is a
material that does not
transfer heat easily.
Examples:
liquids and
gases
jackets
pots handles
10. A cooler (a thermos) is an
insulator.
The molecules in
an insulator are
far apart. This
helps prevent
heat from flowing
in or out.
11. Thermal Equilibrium
Two bodies are said to be at thermal equilibrium if they are at the same
temperature. This means there is no net exchange of thermal energy
between the two bodies. The top pair of objects are in contact, but since
they are at different temps, they are not in thermal equilibrium, and
energy is flowing from the hot side to the cold side.
hot coldheat
26 °C 26 °C
No net heat
flow
The two purple objects are at the same temp and, therefore
are in thermal equilibrium. There is no net flow of heat energy
12. Question
What type of heat transfer?
Warm air mass, bringing a change in the weather.
Wire getting hot from an electric appliance.
Heating a room with a fireplace.
Egg cooking in a frying pan.
Roof of a house becoming hot.
