CH8: Thermal Processes Flashcards
what is thermal equilibrium?
a state in which two or more objects have the same temperature and that there is no net transfer of energy between them.
define energy transfer
energy transfer is a process that occurs when particles move from a region of higher temperature to a region of a lower temperature to achieve thermal equilibrium.
list the 3 methods of energy transfer
thermal conduction
convection
radiation
what is thermal conduction?
a process of energy transfer where energy is transferred through the passing on of vibrational motion from one particle to another.
describe how thermal energy passes through the walls of cans
when the outer wall gains energy from the surroundings, the particles of the can closest to the can vibrate vigorously and collide with neighbouring particles, transferring part of the energy to them. this causes the neighbouring particles to also vibrate vigorously. this process continues from the outer wall to the inner wall.
what happens when heat is supplied to a non-metallic rod?
energy is transferred to the rod by heating. the particles nearest to the heat source gain energy in the kinetic store and vibrate vigorously about their fixed positions. these more energetic particles collide with less energetic neighbouring particles towards the right, transferring part of their energy and causing the neighbouring particles to vibrate vigorously as well.
why are metals a better thermal conductor than non-metals.
metals have free electrons that move at high speeds and transfer energy easily. when the rod is heated, the free electrons gain energy from interacting with particles, which speeds up the process as it allows them to move easily and quickly to the other end of the rod and transfer energy to the particles there. the particles on the cooler side of the rod then vibrate more vigorously.
why are solids better thermal conductors than liquids and gases?
the particles in solids are closely packed which allows energy to be transferred quickly from one particle to the next. this is different from liquids as the particles in liquids are less closely packed which means that the collisions with one another are less frequent. in gases, the particles are far apart from each other and their collisions are even less frequent. therefore, in fluids, the transfer of energy from more energetic particles to less energetics particles by collision is slower, making them less efficient conductors.
define convection
the process of energy transfer by means of convection currents of a fluid due to a difference in density. it only occurs in liquids and gases and not in solids because convection involves bulk movement of the fluid whereas the particles in solids are in fixed positions.
describe the process that happens when liquid is heated
the liquid in the lower region expands and its density decreases, allowing it to rise to the upper region. the surrounding denser colder water from the upper region sinks and displaces the lower region, thus setting up a convection current.
explain why thermal energy cannot be conducted effectively through the air between a heater and a wall.
air is a poor thermal conductor, which means that it transfers energy at a slow rate.
define radiation
the process of energy transfer by electromagnetic waves and does not require a medium. (it can take place in a vacuum)
what is radiation affected by?
surface temperature, surface area, colour and texture
how is radiation affected by surface temperature?
the higher the surface temperature, the higher an object emits radiation, the higher the rate of temperature decreases.
how is radiation affected by surface colour and texture?
the greater the surface area, the higher the rate of energy transfer by radiation.
