2. What is the difference between a poor and a good thermal conductor?
Answers
Answer:
good conductors are the materials which allow electricity to pass them easy whereas, bad conductors are the materials which does not electricity pass them through easy whereas. good conductors example glass, wood. bad conductors examples copper, silver.
Answer:
Metals and stone are considered good conductors since they can speedily transfer heat, whereas materials like wood, paper, air, and cloth are poor conductors of heat.
The Science of Heat Transfer: What Is Conduction?
Heat is an interesting form of energy. Not only does it sustain life, make us comfortable and help us prepare our food, but understanding its properties is key to many fields of scientific research. For example, knowing how heat is transferred and the degree to which different materials can exchange thermal energy governs everything from building heaters and understanding seasonal change to sending ships into space.
Heat can only be transferred through three means: conduction, convection and radiation. Of these, conduction is perhaps the most common, and occurs regularly in nature. In short, it is the transfer of heat through physical contact. It occurs when you press your hand onto a window pane, when you place a pot of water on an active element, and when you place an iron in the fire.
This transfer occurs at the molecular level — from one body to another — when heat energy is absorbed by a surface and causes the molecules of that surface to move more quickly. In the process, they bump into their neighbors and transfer the energy to them, a process which continues as long as heat is still being added.
A temperature gradient is a physical quantity that describes in which direction and at what rate the temperature changes in a specific location. Temperature always flows from the hottest to coldest source, due to the fact that cold is nothing but the absence of heat energy. This transfer between bodies continues until the temperature difference decays, and a state known as thermal equilibrium occurs.
Last, but certainly not least, is the physical properties of the materials involved. Basically, when it comes to conducting heat, not all substances are created equal. Metals and stone are considered good conductors since they can speedily transfer heat, whereas materials like wood, paper, air, and cloth are poor conductors of heat.
Conduction, as demonstrated by heating a metal rod with a flame. Credit: Thomson Higher Education
Conduction, as demonstrated by heating a metal rod with a flame. Credit: Thomson Higher Education
These conductive properties are rated based on a “coefficient” which is measured relative to silver. In this respect, silver has a coefficient of heat conduction of 100, whereas other materials are ranked lower. These include copper (92), iron (11), water (0.12), and wood (0.03). At the opposite end of the spectrum is a perfect vacuum, which is incapable of conducting heat, and is therefore ranked at zero.
Materials that are poor conductors of heat are called insulators. Air, which has a conduction coefficient of .006, is an exceptional insulator because it is capable of being contained within an enclosed space. This is why artificial insulators make use of air compartments, such as double-pane glass windows which are used for cutting heating bills. Basically, they act as buffers against heat loss.
Feather, fur, and natural fibers are all examples of natural insulators. These are materials that allows birds, mammals and human beings to stay warm. Sea otters, for example, live in ocean waters that are often very cold and their luxuriously thick fur keeps them warm. Other sea mammals like sea lions, whales and penguins rely on thick layers of fat (aka. blubber) – a very poor conductor – to prevent heat loss through their skin.
This view of the nose, the forward underside and crew cabin of the space shuttle Discovery was provided by an Expedition 26 crew member during a survey of the approaching STS-133 vehicle prior to docking with the International Space Station. Credit: NASA
This view of the nose section of space shuttle Discovery, build of heat-resistance carbon-composites. Credit: NASA
This same logic is applied to insulating homes, buildings, and even spacecraft. In these cases, methods involve either trapped air pockets between walls, fiber-glass (which traps air within it) or high-density foam. Spacecraft are a special case, and use insulation in the form of foam, reinforced carbon composite material, and silica fiber tiles. All of these are poor conductors of heat, and therefore prevent heat from being lost in space and also prevent the extreme temperatures caused by atmospheric reentry from entering the crew cabin.
The laws governing conduction of heat are very similar to Ohm’s Law, which governs electrical conduction. In this case, a good conductor is a material that allows electrical current (i.e. electrons) to pass through it without much trouble. An electric insulator, by contrast, is any material whose internal electric charges do not flow freely, and therefore make it very hard to conduct an electric current under the influence of an electric field.