Transfer of Thermal Energy Flashcards
when does net transfer of thermal energy occur?
when there is a difference in temperatures
which region to which region does net thermal energy flow from?
from a region of higher temperature to a region of lower temperature
what does thermal equilibrium mean?
it means that there is no net transfer of heat. objects in contact have the same temperature.
define conduction
the transfer of thermal energy through a medium without any flow of the medium.
in what state does conduction typically take place in?
solids
how does conduction work?
particles at heated end vibrate vigorously; collide with neighbouring particles and transfer their energy; particles at cooler end are also set into vigorous vibration.
why are metals better conductors of heat?
metals are better conductors than non-metals as metals have free mobile ions.
how is thermal energy transferred in non-metals?
through vibration and collision of particles only.
how is thermal energy transferred in metals?
through vibration and collision of particles; through electron diffusion.
electrons gain kinetic energy and move more rapidly, colliding with atoms in the cooler parts of the metal and passing their energy on in the process.
why are liquids and gases the worser conductors of heat?
liquid particles further apart and collisions between particles less frequent. frequency of collisions even lower in gases.
therefore, transfer of kinetic energy from fast moving particles to neighbouring particles generally slower in liquids and slowest in gases.
in what state does convection typically take place in?
liquids
define convection
transfer of thermal energy by means of convection currents in a fluid (liquid or gas), due to difference in density.
what is the difference between conduction and convection?
thermal energy transferred from one particle to another by vibration and collision in conduction. particles do not move from fixed positions.
thermal energy transferred through actual movement of heated particles from warmer to cooler parts of fluid in convection. hotter part of fluid flows to cooler part of fluid.
therefore, convection cannot take place in solids because solids cannot flow.
how does convection work?
water at bottom of flask is heated–> expands.
expanded water less dense than surrounding water–> rises
since upper region cooler, it is denser and therefore sinks
difference in densities of water in different regions sets up a convection current.
(if any arrows in the diagram) this is shown by arrows rising from bottom and sinking at the sides.
sea breeze convection example
in the day, the land heats up faster than sea. air above land that is heated, expands and rises.
cool air above sea is denser and moves in to replace warmer air.
this sets up a sea breeze.
land breeze convection example
at night, the land cools faster than the sea.
air above land now cooler and denser than air above sea. it moves out to replace warmer air rising above sea.
this sets up a land breeze.
define radiation
the transfer of thermal energy in the form of electromagnetic waves such as infrared radiation without the aid of a medium
what is infrared radiation?
all bodies emit infrared radiation. infrared radiation does not require a medium to be transmitted. it can travel through vacuum.
how is the earth warmed by the sun?
through infrared radiation
a good emitter of radiation is also
a good absorber of radiation
what factors affect the rate of emission or absorption of radiation by an object?
colour and texture of surface, difference btw surface temp. and surroundings’ temp. and its surface area
to obtain a higher rate of radiation, what is needed for the factor: colour and texture of surface?
dull, black, rough
to obtain a higher rate of radiation, what is needed for the factor: difference btw object’s surface temp. and surroundings’ temp.
larger temp. diff.
to obtain a higher rate of radiation, what is needed for the factor: surface area?
larger surface area
