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Physics/Conduction

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Question
What does it mean when something is conductive? I think metal is conductive because it allows electricity to easily travel within it and across wire, while something like water is a poor conductor that doesn't easily let electricity pass from one terminal to the other. How does this concept relate to heat? If a material is conductive to heat it allows heat to pass through it? Is that the opposite of being a good insulator? I was asking someone about how well plexiglas and polycarbonate could insulate heat to keep it on one side of it and someone used the word conductive when talking about it, and I wasn't sure if they meant it as being somehow the same as a good insulator. What does it mean for something to be a good conductor of heat?

Answer
Hello James,

There are 2 kinds of conductivity. It might be the ability to conduct electricity or conduct heat. I need to clarify something you said. Pure water is a poor electrical conductor. But tap water conducts electricity quite well.

To say something is conductive, it means it conducts heat or electricity (whichever you're talking about) without putting up a big fight about it. Everything provides at least a small amount of resistance to allowing electricity to pass through it. There will always be at least a slight difference in the voltage at the 2 ends of a path that a current is flowing through. Some things, like rubber, put up a large amount of resistance to the flow of current.

If heat is passing from one surface of a material to the opposite surface, there will always be a difference between the temperature of those surfaces. A material that is a poor conductor (you can also describe it as a good insulator) can have a large temperature difference between those 2 surfaces with little heat passing to the cooler side. If the material is a good heat conductor, there will be a relatively small temperature difference, and much more heat passing to the cool surface, in the above situation.

Many materials that conduct electricity well also conduct heat well. But not all. Both pure water and tap water conduct heat quite well.

You asked:
If a material is conductive to heat it allows heat to pass through it? True, and it allows heat to pass through more easily than the average material.

Is that the opposite of being a good insulator? Yes, a good insulator does a good job of resisting the flow of heat or electricity (whichever you're talking about). Being a good conductor is the opposite of being a good insulator.

What does it mean for something to be a good conductor of heat? If you have a Styrofoam cup, you can't easily feel the temperature of the liquid inside. If you have a tin cup, you can easily feel the temperature of the liquid inside. The Styrofoam insulates you from the hot coffee inside. Same with the insulation in a house. It can be cold outside but the inside surface of the walls of your home is warm because there is insulation between the inside and outside surfaces of the wall.

I hope this helps,
Steve

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Steve Johnson

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I would be delighted to help with questions up through the first year of college Physics. Particularly Electricity, Electronics and Newtonian Mechanics (motion, acceleration etc.). I decline questions on relativity and Atomic Physics. I also could discuss the Space Shuttle and space flight in general.

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I have a BS in Physics and an MS in Electrical Engineering. I am retired now. My professional career was in Electrical Engineering with considerable time spent working with accelerometers, gyroscopes and flight dynamics (Physics related topics) while working on the Space Shuttle. I gave formal classroom lessons to technical co-workers periodically over a several year period.

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BS Physics, North Dakota State University
MS Electrical Engineering, North Dakota State University

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