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Chapter 17: Heat & Its Transmission

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Transcript of Chapter 17: Heat & Its Transmission

Movement of heat
Conduction
Conduction is the process of heat transfer through a medium or material without any movement of the medium or materials.


All matters are made up of atoms and molecules, hence when an object is heated, the particles will start to gain energy and vibrate more vigorously resulting the particles to bump into other neighbouring particles and transfer of their energy to them. This then continues and passes the energy from the hot end down to the colder end of the object.
applications
Movement of heat
Heat flows from a region of a higher temperature to a region of lower temperature.
The movement of heat occurs through one or more of the following processes:
Conduction
Convection
Radiation

radiation
here is a quick summary of radiation;
Good
conductors of heat
Copper
Aluminium
Iron
Silver
eg: kettles made of sliver,
applications of conduction
for example; the miner's safety lamp is made of metal. the metal gauze conducts heat away quickly from a naked flame inside it, so that flammable gases outside never get hot enough to catch fire.
Convection
How conduction of heat takes place
Bad
conductors of
heat
Plastic
Rubber
Glass
Wood
eg: wooden spoons,
Convection is the transfer of heat from one place to another by the movement of fluids. ( ONLY in liquids and gases )
How convection takes place
A fluid of lower density rises in a fluid of higher density. A fluid will sink when it is in a fluid of lower density. Convection takes place due to the expansion of liquid. Hence, when a fluid is hot, its volume increases. Thus, its density decreases causing the less dense fluid to rise resulting the denser liquid to sink.
Why convection only occurs in liquids
Particles in solids are arranged closely and in a regular pattern. Hence, they are unable to move freely and transfer heat from one point to another. Whereas, particles in fluids are arranged slightly apart and in an irregular pattern. Thus, they are able to slide over one another transferring heat from one point to another.
radiation is the transfer of heat in the form of heat waves from one place to another that does not require a medium for transmission.
heat loss/gain is affected by
nature of surface: the darker/rougher surface is, the higher the rate of radiation or absorption
surface area: the greater the area, the higher rate of radiation or absorption
temperature: the hotter the body, the higher rate of radiation
applications of convection
electric kettle

the heating coil of the kettle is placed near the base of the kettle
this makes boiling more efficient as water becomes less dense and rises when it is heated . this allows convection currents to be set up easily during heating.
vacuum flask
a hot liquid in a vacuum flask stays hot because the vacuum flask is designed to reduce heat loss from the liquid by conduction, convection and radiation
the cap;
is usually made of a
poor conductor of heat
,such as plastic
the cork stopper;
the stopper using a
bad conductor of heat.
the stopper also prevent
heat loss
through convection into
the surroundings

slivered glass walls;
the silver colour reduces
radiation
vacuum;
the vacuum is created between the walls by removing air. conduction and convection cannot take place in an vacuum
the red arrows indicate the hot fluid and the blue arrows indicate the cold fluids
diagram A shows the hot liquid rising up due to its lower density while diagram B shows the convection current
good conductors have the presence of free electrons while poor conductors trap air
here is an example of convection in water
this was done by : bless, narisa, shih kean and jingjie of 2 em.
applications of radiation
the earth gets energy from the sun in the form of sunlight. the earth's surface absorbs some of this energy and heats up. the earth cools down by giving off a different form of energy, called infrared radiation.
here is a video on the greenhouse effect as an application of radiation
Full transcript