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Heat (Charlotte) - Coggle Diagram
Heat (Charlotte)
convection
a process of heat transfer through a medium by the movement of particles in the medium
can only take place in liquids and gases
why?
Convection requires the movement of particles in the medium. The particles in liquids and gases are able to move freely, so they can transfer heat from one region to another by convection. However, then particles in solids and vacuums are unable to move freely as they can only vibrate at their fixed positions
movement of particles in a convection current
When a region of the fluid is heated, the particles move faster and spread apart. The volume of the region increases but the mass of the particles remains constant. Hence, its density decreases.
hot water rises and cold water sinks
convection in liquids and gases
liquids
as water is heated, it expands and the density decreases and rises up. the cooler part of the water, which is denser, sinks in to replace the heated water, it is in turn heated and risen.
gases
air above the lit candle is heated and expanded. as a result, the density decreases and it rises out of the chimney. The cooler surrounding air is denser at the other chimney so it sinks the replace the rising hot air.
applications in daily lives
electric kettle (heating element)
the heating element is placed at the bottom of the kettle. when it is turned on, it heats up water at the bottom. hot water rises and cold water sinks
hot water system (boiler)
boiler is placed at the lower part of the system. when heated, hot water rises to the cold part of the storage tank and cold water sinks into the boiler
convection in natural phenomena
sea breeze (during the day)
during the day, the land is heated up faster than the sea. the air above the land is warmer than above the sea, so it rises up. the cooler and denser air from the sea is replaced with the rising hot air.
land breeze (during the night)
during the night, the land loses heat much faster than the sea. the air above the sea is warmer than above the land so it rises up. the cooler and denser air from the land is replaced with the rising hot air.
radiation
the heat transfer by the emission of infrared radiation
does not require a medium
moves in all directions
terms
radiator
objects that give off heat
absorber
objects that take in heat
reflector
objects that bounce off radiation
factors that affect rate of heat transfer by radiation
surface area
surface temperature
color and texture
applications of radiation in daily lives
refrigerator
cooling coils are painted black to ensure that heat is lost quickly, as black can radiate heat faster to the surroundings
white clothes
white is a poor absorber of heat
hot water containers
they have a shiny appearance to reduce heat loss from radiation from inside the containers to the surroundings
conduction
the process of heat transfer through a medium without the movement of particles in the medium
heat is transmitted through
the vibration of particles
in solids, the particles are closely packed together and vibrate at their fixed positions. when heated, the particles gain heat energy and vibrate more vigorously, causing the neighbouring particles to vibrate vigorously too.
motion of free electrons (metals)
During heating, the free electrons help to transfer heat energy from the heated region to a cooler region quickly
applications of conduction in daily lives
good conductors
cooking utensils made of metals (iron, copper, aluminum)
heating element in electric kettles
poor conductors
expansion and contraction
what causes the size of an object to change when heat is transferred to an object?
the particles in an object gain more kinetic energy and push each other further away through their vigorous motion
gases expand and contract faster than solids and liquids
changes in density during expansion and contraction
expansion
the particles in a substance gain heat energy during heating, and their motion increases.
the vigorous motion push each other further apart, increasing the space they occupy
contraction
the particles in a substance lose heat energy during cooling and their motion decreases.
the less vigorous motion makes them become closer to each other, decreasing the space they occupy.
experiments to show expansion in matter
solids (metal ball +ring)
the metal ball cannot pass through the ball at first, after the ring is heated, the ball can pass through
the expansion in solids is caused by their particles pushing each other further apart to occupy more space, so the length of solids increases.
liquids (water level)
the water level drops when it is heated initially, because glass expands first before water, so the volume of the glass increases.
after heating for a while, the water level increases
the expansion in liquids is caused by the particles occupying more space when their motion increases and move further away from each other.
problems & solutions to expansion and contraction
pipes (straight)
pipes carrying hot liquids have curved joints or are coiled
they provide some spaces for the expand or contract to prevent them from breaking easily
bridges (size)
one end of the bridge has a fixed end and the other has a movable joint
the movable joint provides spaces for the bridge to expand or contract