Heat transfer Flashcards
How do we distinguish between good and bad conductors of heat?
Materials that allow heat to pass through them easily are called good conductors of heat. Materials that do not conduct heat as easily and quickly are bad conductors
Describe how by the movement of molecules heat is transferred in solids
When the metal is heated, the first layer of atoms will gain energy and vibrate faster. When the first layer of atoms collides with the second layer, energy is transferred and the second layer will vibrate faster. This will continue until the last layer
Describe how by the movement of electrons heat is transferred in solids
When the metal is heated, the first layer of atoms will gain energy and vibrate faster. When the first layer of atoms collide with the free electrons, these free electrons will move rapidly towards the cooler region and will transfer heat to the distant atoms during collisions.
What are the three methods by which heat can be transferred?
Conduction (in solids)
Convection (in liquids and gases)
Radiation
Define convection
It is the transfer of heat from hot to cold regions in a liquid or gas
Describe how convection occurs
When the liquid/gas is heated, its volume increases due to expansion. Since density is mass÷volume, density of hot water will decrease. Therefore hot water rises and cold water comes down from the sides. This movement is known as convection current
What is radiation?
It is the emission of heat from hot objects. It does not need any medium
By which process does heat reach the Earth from the sun?
Radiation
If a person places his hand near a bulb, he will feel heat. Explain all the processes by which heat from the bulb reaches his hand.
Radiation: Heat is emitted from the hot filament
Convection: Heat transfer from filament to inner wall of bulb
Conduction: Heat transfer from inner wall to outer wall of bulb
Radiation: Heat emitted from bulb
State the observations, conclusions and precautions for the experiment to show black surfaces are better absorbers of heat than white surfaces. labelled diagram
Observations: Cork A will fall faster. This implies that wax on the black surface has melted faster.
Conclusion: Black surfaces are better absorbers of heat.
Precautions: 1) The candle must be placed in the middle. 2) Both rods must have the same thickness
Observations, conclusion and precautions for the experiment to show that black surfaces are better emitters of heat than white/shiny surfaces. labelled diagram
Observation: Temperature of liquid in black metal can, falls faster. This implies that liquid in black metal can loses heat faster.
Conclusion: Black surfaces are better emitters of heat.
Precautions: 1) Both liquids must have the same initial temperature. 2) Identical thermometers should be used. 3) Same volume of water
Describe how to distinguish between good and bad emitters and good and bad absorbers of infrared
radiation
Matt, black surfaces are the best emitters and absorbers; and shiny, light surfaces are the worst emitters and absorbers
Describe how heat is transferred to or from buildings and to or from a room
Heat energy is transferred from homes by conduction through the walls, floor, roof and windows
State and explain the use of the important practical methods of thermal insulation for buildings
Thermal insulation is an important technology to reduce energy consumption in buildings by preventing heat gain/loss through the building envelope.
