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Question
Is there a relationship between electrical conductivity and thermal conductivity?
Asked by: Darell Hayes
Answer
There is a relationship for metals and it is known as the Wiedemann-Franz law. Metals are good electrical conductors because there are lots of free charges in them. The free charges are usually negative electrons, but in some metals, e.g., tungsten, they are positive 'holes.' For purposes of discussion, let's assume we have free electron charges.
When a voltage difference exists between two points in a metal, it creates an electric field which causes the electrons to move, i.e., it causes a current. Of course, the electrons bump into some of the stationary atoms (actually, 'ion cores') of the metal and this frictional 'resistance' tends to slow them down. The resistance depends on the specific type of metal we're dealing with. E.g., the friction in silver is much less than it is in iron. The greater the distance an electron can travel without bumping into an ion core, the smaller is the resistance, i.e., the greater is the electrical conductivity. The average distance an electron can travel without colliding is called the 'mean free path.' But there's another factor at work too. The electrons which are free to respond to the electric field have a thermal speed a sizable percentage of the speed of light, but since they travel randomly with this high speed, they go nowhere on average, i.e., this thermal speed itself doesn't create any current.
The thermal conductivity of this metal is, like electrical conductivity, determined largely by the free electrons. Suppose now that the metal has different temperatures at its ends. The electrons are moving slightly faster at the hot end and slower at the cool end. The faster electrons transmit energy to the cooler, slower ones by colliding with them, and just as for electrical conductivity, the longer the mean free path, the faster the energy can be transmitted, i.e., the greater the thermal conductivity. But the rate is also determined by the very high thermal speed-the higher the speed, the more rapidly does heat energy flow(i.e., the more rapidly collisions occur). In fact, the thermal conductivity is directly proportional to the product of the mean free path and thermal speed.
Both thermal and electrical conductivity depend in the same way on not just the mean free path, but also on other properties such as electron mass and even the number of free electrons per unit volume. But as we have seen, they depend differently on the thermal speed of the electrons-electrical conductivity is inversely proportional to it and thermal conductivity is directly proportional to it. The upshot is that the ratio of thermal to electrical conductivity depends primarily on the square of the thermal speed. But this square is proportional to the temperature, with the result that the ratio depends on temperature, T, and two physical constants: Boltzmann's constant, k, and the electron charge, e. Boltzmann's constant is, in this context, a measure of how much kinetic energy an electron has per degree of temperature.
Putting it all together, the ratio of thermal to electrical conductivity is:
( 2 / 3 ) * ( (k/e)2 ) * T
the value of the constant multiplying T being: 2.45x10-8 W-ohm-K-squared.
http://www.physlink.com/education/AskExperts/ae432.cfm
What else can I help you with?
The difference between conductors and insulators in how they react to electrical charges?
Conductors allow electric charges to flow easily through them due to the presence of free electrons, while insulators do not allow these charges to flow easily because they lack these free electrons. Conductors have low resistance to the flow of electric charges, while insulators have high resistance.
What Materials with electrical characteristics that fall between those of insulators and conductors are considered?
Materials with electrical characteristics that fall between insulators and conductors are known as semiconductors. Semiconductors have an intermediate level of electrical conductivity, making them valuable for use in electronic devices such as transistors and diodes. They can be controlled to act as either insulators or conductors using techniques like doping or applying voltage.
What are the classification of materials according to electrical conductivity?
Most substances fall into two categories - conductors and insulators. Conductors are those which electricity can pass through relatively easily. Metals are the usual example, but other substances such as graphite and polar liquids such as water are also good conductors. Insulators are poor conductors: those that electricity cannot pass through easily. Most plastics are insulators. Some substances fall in between: these are semiconductors, which allow electricity through in some instances, but not in others. This property makes them very useful in electronics. Some substances can be such good conductors that, under some circumstances, they can allow electricity to pass through them with no resistance at all. These are called superconductors.
How do you know the difference between conductors and insulators?
Conductors allow the flow of electricity due to the presence of free electrons, while insulators inhibit electron flow. Conductors often have low resistance, while insulators have high resistance to the flow of electricity. Materials such as metals are good conductors, while materials such as rubber are good insulators.
What is open wiring insulators?
Open wiring insulators are devices used to separate and support electrical conductors in open wiring installations. They are usually made of ceramic or plastic and are designed to prevent the flow of electricity between conductors and the surrounding environment, reducing the risk of electrical hazards. These insulators help to maintain the integrity and safety of the wiring system.
The difference between conductors and insulators in how they react to electrical charges?
Conductors allow electric charges to flow easily through them due to the presence of free electrons, while insulators do not allow these charges to flow easily because they lack these free electrons. Conductors have low resistance to the flow of electric charges, while insulators have high resistance.
What Materials with electrical characteristics that fall between those of insulators and conductors are considered?
Materials with electrical characteristics that fall between insulators and conductors are known as semiconductors. Semiconductors have an intermediate level of electrical conductivity, making them valuable for use in electronic devices such as transistors and diodes. They can be controlled to act as either insulators or conductors using techniques like doping or applying voltage.
What the difference of electrical materials?
Electrical materials can be classified into conductors, insulators, and semiconductors based on their ability to conduct electricity. Conductors, like copper and aluminum, allow electricity to flow freely due to their low resistance. Insulators, such as rubber and glass, prevent electrical flow and are used to protect against electrical shocks. Semiconductors, like silicon, have properties between conductors and insulators, allowing them to conduct electricity under certain conditions, making them essential for modern electronics.
What are the classification of materials according to electrical conductivity?
Most substances fall into two categories - conductors and insulators. Conductors are those which electricity can pass through relatively easily. Metals are the usual example, but other substances such as graphite and polar liquids such as water are also good conductors. Insulators are poor conductors: those that electricity cannot pass through easily. Most plastics are insulators. Some substances fall in between: these are semiconductors, which allow electricity through in some instances, but not in others. This property makes them very useful in electronics. Some substances can be such good conductors that, under some circumstances, they can allow electricity to pass through them with no resistance at all. These are called superconductors.
How do you know the difference between conductors and insulators?
Conductors allow the flow of electricity due to the presence of free electrons, while insulators inhibit electron flow. Conductors often have low resistance, while insulators have high resistance to the flow of electricity. Materials such as metals are good conductors, while materials such as rubber are good insulators.
What is open wiring insulators?
Open wiring insulators are devices used to separate and support electrical conductors in open wiring installations. They are usually made of ceramic or plastic and are designed to prevent the flow of electricity between conductors and the surrounding environment, reducing the risk of electrical hazards. These insulators help to maintain the integrity and safety of the wiring system.
What is the main way that the structure of an insulator differs from the structure of a conductor?
The main difference between the structure of an insulator and a conductor is in the arrangement of their electrons. Insulators have tightly bound electrons that are not free to move easily, while conductors have loosely bound electrons that can move freely in response to an applied electric field. This difference in electron mobility is what leads to the contrasting electrical properties of insulators and conductors.
What is the difference between insulators and conductors of heat and electricity?
Insulators are materials that do not allow heat or electricity to flow easily through them, whereas conductors are materials that allow heat or electricity to flow easily. Insulators have high resistance to the flow of heat or electricity, while conductors have low resistance. Examples of insulators include rubber and wood, while examples of conductors include metals like copper and aluminum.
What are the differences between insulators and conductors?
Insulators are materials that do not allow the flow of electricity, while conductors are materials that allow the flow of electricity. Conductors have low resistance to electrical flow, while insulators have high resistance. Examples of insulators include rubber and plastic, while examples of conductors include metals like copper and silver.
What is the difference between good conductors and good insulators?
Conductors are good energy carriers they allow energy to pass through them easily examples are steel,metals and cooper. Insulators do not allow energy (or heat) to pass through them easily such examples are wood oven mitts and cloth. ..... unless the person asking the question was referring to electricity. I dont think wood, oven mitts and cloth would be good examples for electrical insulators, as they are susceptible to collecting moisture, which is an electrical carrier.
How do use conductors and insulators when building a circuit?
The circuit and its mechanical layout are designed in such a way thatconductors are used between points where current is intended to flowwith as little loss of energy as possible, and insulators are positionedin all locations through which current is not supposed to flow.
Are scissors conductors?
They are Conductors, not much for insulation though. Differences between conductors and insulators? Conductors let energy such as electricity .
