Definition of Conductivity
Conductivity can refer to thermal, acoustic, or electric charge transfer. These three properties are sometimes related. For example, metals are good at all three. However, when one speaks of a "conductor" without context, it usually means "electrical conductor."
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Definition
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In physics, conductivity is a measure of the ability to transfer heat, sound, or electric charge. These abilities can be defined mathematically in terms of the variables that affect them, such as density and electron mobility.
Electrical Conductivity
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Electrical conductivity is technically defined as the reciprocal of the resistivity. The resistivity is a little different from the resistance, but related, being defined as the current-induced electric field at a point in the conductor divided by the current density.
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Acoustic Conductivity
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The speed of sound through a substance can be used as a measure of acoustic conductivity. The speed of sound decreases with compressibility, because it serves to dampen the sound waves.
Thermal Conductivity
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Thermal conductivity is defined as the heat that flows through the conductor per unit time. Thermal conductivity is proportional to the conductor's cross-section and inversely proportional to its length, just as water can flow faster through a wide, short tunnel.
What's Special About Metal
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The high electron mobility in most metals (the "transition" metals in particular) gives them comparatively good thermal and electrical conductivity. This is because their structure is like atoms in a sea of electrons, not permanently confined to any given inter-atomic bond.
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