physics chapter 10 Flashcards
what is thermal energy
always flows from a region of higher temperature to a region of lower temperature
what is the difference in temperature
net flow of thermal energy
what is conduction
transfer of thermal energy through solids
what is the thermal conductivity of a material
depends on how quickly thermal energy is transferred from the hotter end to the colder end
what do the good thermal conductors do
transfer thermal energy quickly
what do bad thermal conduction do
transfer thermal energy slowly
what is a bad thermal conductor also called
insulator
state some of the materials in order that are considered as the best conductors to the worst conductors of thermal energy
diamond, copper, steel, ice, polythene, fibreglass, polystyrene and air
state some of the materials in order that are considered as the best insulators to the worst insulators of thermal energy
air, polystyrene, fibreglass, polythene, ice, steel, copper and diamond
how can we investigate the transfer of thermal energy through solids
- for the drawing of the pins to fall, the wax on the four rods must melt. the wax is melted because thermal energy was transferred from the ends of the rods heated by the bunsen burner to the ends of the rods at room temperature. the transfer of thermal energy through the rods occurred without any flow of the material the rods were made of. this means that the thermal energy was transferred by conduction
- the time taken for the drawing of the pins to fall for each of the four rods was different. this shows that different materials conduct thermal energy at different rates. the time taken is the shortest copper is the best and glass is the worst thermal conductor among the four materials
how does conduction work in metals
through lattice vibrations of particles and movement of free electrons
how does conduction work in non metals
only lattice vibrations of particles take place
why are liquids and gases bad thermal conductors
particles in liquids and gases are spaced further apart than those in solids. collisions between the particles in liquids and gases are less frequent. transfer of kinetic energy from the fast moving particles to neighbouring particles is slower. therefore, air and water are bad thermal conductors
what is convection
transfer of thermal energy in a fluid by means of convection currents due to a difference in density
describe convection
- convection currents only occur in fluids not in solids
- this is because convection involves the bulk movement of the fluid that carries the thermal energy. this means that for convection currents to occur in a substance, the substance must be able to flow
- in solids, the particle are held in fixed positions, hence the solid cannot flow. they can only transfer thermal energy from one particles to another through lattice vibrations
how do liquids and gases transfer thermal energy
- the incense stick is used to produce smoke that trace the convection currents.
- the candle below the chimney on the right is lit. the incense stick is held over the left chimney. the smoke is drawn down across the right chimney and rises up above the candle. this shows the circulating convection currents in the air
why do convection currents form
convection currents form because of the difference in density in air when heated.
what is conduction
still occurs in liquids, but is much slower compared to convection
what is thermal radiation
transfer of thermal energy in the form of invisible waves which can travel through a vacuum.
what is thermal radiation
it is also known as infrared radiation. all objects absorb and emit infrared radiation. invisible radiation that carries thermal energy
how can we investigate the emission of difference surfaces
dull and black surfaces emit infrared radiation at a faster rate than shiny and silver surfaces
how can we investigate the absorption of different surfaces
dull black surfaces absorb infrared radiation at a faster rate than shiny silver surfaces
what factors affect the emission and absorption of thermal radiation
- high surface temperature
- larger surface area
what factors affection the emits the absoprtion affect the temperature of an object
- infrared radiation abosrbs, the object warms up
- infrared radiation absorbed, the radiation in objects cool down
