Understanding Electrical, Thermal, and Sound Conductors

In science, a conductor is a material that permits a flow of energy. A material that allows the flow of charged particles is an electrical conductor. A material that enables the transfer of thermal energy is a thermal conductor or heat conductor. Although electrical conductivity and thermal conductivity are most common, other types of energy may be transferred. For example, a material that allows the passage of sound is a sonic (acoustic) conductor (sonic conductance relates to fluid flow in engineering).

Conductor vs. Insulator

While a conductor transmits energy, an insulator slows or stops its passage. Some materials can be both a conductor and an insulator at the same time for different forms of energy. For example, most diamonds conduct heat exceptionally well, yet they are electrical insulators. Metals conduct heat, electricity, and sound.

Electrical Conductors

Electrical conductors transmit electrical charge in one or more directions. Any charged particle may be transmitted, however, since electrons surround atoms, while protons are usually bound within the nucleus, it's much more common for electrons to move than protons. Either positive or negative charged ions also can transfer charge, as in seawater. Charged subatomic particles may also move through certain materials.

How well a given material allows charge flow depends not only on its composition but also on its dimensions. A thick copper wire is a better conductor than a thin one; a short wire conducts better than a long one. Opposition to the flow of charge is called electrical resistance. Most metals are electrical conductors.

Some examples of excellent electrical conductors are:

• Silver
• Gold
• Copper
• Seawater
• Steel
• Graphite

Examples of electrical insulators include:

• Glass
• Most Plastics
• Pure Water

Thermal Conductors

Most metals are also excellent thermal conductors. Thermal conductivity is heat transfer. This occurs when subatomic particles, atoms, or molecules gain kinetic energy and collide with each other.

Thermal conduction always moves in the direction of highest to lowest heat (hot to cold) and depends not only on the nature of the material but also on the temperature difference between them. Although thermal conductivity occurs in all states of matter, it's greatest in solids because particles are packed more closely together than in liquids or gases. 

Examples of good thermal conductors include:

• Steel
• Mercury
• Concrete
• Granite

Examples of thermal insulators include:

• Wool
• Silk
• Most Plastics
• Insulation
• Feathers
• Air
• Water

Sound Conductors

Transmission of sound through a material depends on the density of the matter because sound waves require a medium to travel. So, higher density substances are better sound conductors than low-density materials. A vacuum cannot transfer sound at all.

Examples of good sound conductors include:

• Lead
• Steel
• Concrete

Examples of poor sound conductors would be:

• Feathers
• Air
• Cardboard