On this page, you will learn how thermal energy move through solids. This mechanism of heat transfer is called conduction. You will learn what affects the rate of heat flow through conduction.
Conduction
Learning goal
❶ Different materials have different thermal conductivities
Some materials conduct heat faster than others. For example, wood feels warmer than metal because heat conduction
happens more slowly in wood than in metal. The ability of a material to conduct heat is called
thermal conductivity.
The following simulation shows a comparison of heat conduction in wood and metal.
Instructions: A race of heat conduction
Two cold objects at 0°C are connected to two hot objects at 50°C through two slabs made of
wood and metal, respectively. Two thermometers are placed in the middle of the cold objects to
monitor the increasing of temperature. Their readings are shown in the graph that can be turned on
by clicking Graph "On". When the graph is shown, clicking a thermometer will highlight its temperature
curve. Click "Run" to start the simulation.
Important: The increased temperatures ΔT measured by the thermometers placed on the cold objects
in the simulation reflect the heat Q transferred from the hot objects, because
Q=mCΔT
where m is the mass of the cold object and C is its specific heat capacity. Therefore, the higher
the temperature rises, the more thermal energy flows.
❷ The size of the conductive area matters
The flow of thermal energy in a solid is also affected by the size of the conductive area. In the following
simulation, you will explore this effect.
Instructions:
This simulation has a similar setup with the previous one, except that the two slabs are made of identical material
(i.e., they have the same thermal conductivity) and the upper slab is much thinner than the lower one.
Question: (Click the link below to answer)
Which slab conducts heat faster?
❸ The difference of temperature matters
The flow of thermal energy from a hot object to a cold object also depends on the difference of temperature between
them.
Instructions:
This simulation has a similar setup as the first one on this page, except that the temperature of the
upper hot object is twice as much as that of the lower hot object and the two slabs in the middle are
made of the same material (i.e., they have the same thermal conductivity).
Question: (Click the link below to answer)
Which cold object heats up more quickly?
❹ The heat capacity of the conductive area matters
The flow of thermal energy is affected by the heat capacity of the conductive area.
Instructions:
This simulation has a similar setup as the first one on this page, except that the upper slab
has a much lower heat capacity than the lower one. The thermal conductivities of the two are identical.
Click "Run" to start the simulation and observe the
speed of heat conduction in the two slabs.
Question: (Click the link below to answer)
Describe and explain the result of this simulation.
Summary
The amount of thermal energy ΔQ transferred through an area A in a time period Δt is called the heat flux.
In the case of conduction, heat flux is determined by the following relationship:
ΔQ/Δt=-kAΔT/Δx
where ΔT is the temperature difference along a distance Δx in the direction of conduction,
and k is the thermal conductivity of the material. This is known as Fourier's Law of Heat Conduction.
Question: (Click the link below to answer)
Explain Fourier's Law of Heat Conduction based on the above four simulations.
| Some materials conduct heat faster than others. For example, wood feels warmer than metal because heat conduction happens more slowly in wood than in metal. The ability of a material to conduct heat is called thermal conductivity. The following simulation shows a comparison of heat conduction in wood and metal. | |||
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| The flow of thermal energy in a solid is also affected by the size of the conductive area. In the following simulation, you will explore this effect. | |||
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| The flow of thermal energy from a hot object to a cold object also depends on the difference of temperature between them. | |||
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| The flow of thermal energy is affected by the heat capacity of the conductive area. | |||
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The amount of thermal energy ΔQ transferred through an area A in a time period Δt is called the heat flux.
In the case of conduction, heat flux is determined by the following relationship:
ΔQ/Δt=-kAΔT/Δx where ΔT is the temperature difference along a distance Δx in the direction of conduction, and k is the thermal conductivity of the material. This is known as Fourier's Law of Heat Conduction. Question: (Click the link below to answer) Explain Fourier's Law of Heat Conduction based on the above four simulations. |